diff --git a/src/compute.cpp b/src/compute.cpp
index f3b24f7bbc..eb01566132 100644
--- a/src/compute.cpp
+++ b/src/compute.cpp
@@ -32,10 +32,16 @@ using namespace LAMMPS_NS;
 #define DELTA 4
 #define BIG MAXTAGINT
 
+// allocate space for static class instance variable and initialize it
+
+int Compute::instance_total = 0;
+
 /* ---------------------------------------------------------------------- */
 
 Compute::Compute(LAMMPS *lmp, int narg, char **arg) : Pointers(lmp)
 {
+  instance_me = instance_total++;
+
   if (narg < 3) error->all(FLERR,"Illegal compute command");
 
   // compute ID, group, and style
diff --git a/src/compute.h b/src/compute.h
index 9344eb92f5..631507bda3 100644
--- a/src/compute.h
+++ b/src/compute.h
@@ -20,6 +20,8 @@ namespace LAMMPS_NS {
 
 class Compute : protected Pointers {
  public:
+  static int instance_total;     // # of Compute classes ever instantiated
+
   char *id,*style;
   int igroup,groupbit;
 
@@ -122,6 +124,8 @@ class Compute : protected Pointers {
   virtual int unsigned data_mask_ext() {return datamask_ext;}
 
  protected:
+  int instance_me;             // which Compute class instantiation I am
+
   int extra_dof;               // extra DOF for temperature computes
   int fix_dof;                 // DOF due to fixes
   int dynamic;                 // recount atoms for temperature computes
diff --git a/src/fix.cpp b/src/fix.cpp
index e904809a1b..2ec28be0a5 100644
--- a/src/fix.cpp
+++ b/src/fix.cpp
@@ -23,10 +23,16 @@
 using namespace LAMMPS_NS;
 using namespace FixConst;
 
+// allocate space for static class instance variable and initialize it
+
+int Fix::instance_total = 0;
+
 /* ---------------------------------------------------------------------- */
 
 Fix::Fix(LAMMPS *lmp, int narg, char **arg) : Pointers(lmp)
 {
+  instance_me = instance_total++;
+
   // fix ID, group, and style
   // ID must be all alphanumeric chars or underscores
 
diff --git a/src/fix.h b/src/fix.h
index 77c1b5322f..04920df238 100644
--- a/src/fix.h
+++ b/src/fix.h
@@ -20,6 +20,8 @@ namespace LAMMPS_NS {
 
 class Fix : protected Pointers {
  public:
+  static int instance_total;     // # of Fix classes ever instantiated
+
   char *id,*style;
   int igroup,groupbit;
 
@@ -199,6 +201,8 @@ class Fix : protected Pointers {
   virtual unsigned int data_mask_ext() {return datamask_ext;}
 
  protected:
+  int instance_me;        // which Fix class instantiation I am
+
   int evflag;
   int vflag_global,vflag_atom;
   int maxvatom;
diff --git a/src/neigh_list.cpp b/src/neigh_list.cpp
index 0de4c0cb5f..47eb34bb86 100644
--- a/src/neigh_list.cpp
+++ b/src/neigh_list.cpp
@@ -224,6 +224,8 @@ void NeighList::print_attributes()
   NeighRequest *rq = neighbor->requests[index];
 
   printf("Neighbor list/request %d:\n",index);
+  printf("  %p = requestor ptr (instance %d id %d)\n",
+         rq->requestor,rq->requestor_instance,rq->id);
   printf("  %d = build flag\n",buildflag);
   printf("  %d = grow flag\n",growflag);
   printf("  %d = stencil flag\n",stencilflag);
diff --git a/src/neigh_request.cpp b/src/neigh_request.cpp
index 95ddc01517..5f47bf5da4 100644
--- a/src/neigh_request.cpp
+++ b/src/neigh_request.cpp
@@ -90,7 +90,7 @@ void NeighRequest::archive()
 
 /* ----------------------------------------------------------------------
    compare this request to other request
-   identical means all params set by requester are the same
+   identical means all params set by requestor are the same
    compare to original values in other if Neighbor may have changed them
    return 1 if identical, 0 if not
 ------------------------------------------------------------------------- */
@@ -100,10 +100,15 @@ int NeighRequest::identical(NeighRequest *other)
   int same = 1;
 
   // set same = 0 if old list was never processed
-
+  // use of requestor_instance and instance counter
+  //   prevents an old fix from being unfix/refix in same memory location
+  //   and appearing to be old, when it is really new
+  //   only needed for classes with persistent neigh lists: Fix, Compute, Pair
+  
   if (other->unprocessed) same = 0;
 
   if (requestor != other->requestor) same = 0;
+  if (requestor_instance != other->requestor_instance) same = 0;
   if (id != other->id) same = 0;
 
   if (pair != other->pair) same = 0;
diff --git a/src/neigh_request.h b/src/neigh_request.h
index 41fa951fee..53ca2b797c 100644
--- a/src/neigh_request.h
+++ b/src/neigh_request.h
@@ -20,11 +20,12 @@ namespace LAMMPS_NS {
 
 class NeighRequest : protected Pointers {
  public:
-  void *requestor;       // class that made request
-  int id;                // ID of request
-                         // used to track multiple requests from one class
-  int unprocessed;       // 1 when first requested
-                         // 0 after processed by Neighbor class
+  void *requestor;          // class that made request
+  int requestor_instance;   // instance of that class (only Fix, Compute, Pair)
+  int id;                   // ID of request as stored by requestor
+                            // used to track multiple requests from one class
+  int unprocessed;          // 1 when first requested
+                            // 0 after processed by Neighbor class
 
   // which class is requesting the list, one flag is 1, others are 0
 
@@ -100,7 +101,7 @@ class NeighRequest : protected Pointers {
 
   int otherlist;         // index of other list to copy or skip from
 
-  // original params by requester
+  // original params by requestor
   // stored to compare against in identical() in case Neighbor changes them
 
   int half_original;
diff --git a/src/neighbor.cpp b/src/neighbor.cpp
index faf3f01a0f..f9389a47cf 100644
--- a/src/neighbor.cpp
+++ b/src/neighbor.cpp
@@ -908,7 +908,7 @@ void Neighbor::init()
 
 /* ---------------------------------------------------------------------- */
 
-int Neighbor::request(void *requestor)
+int Neighbor::request(void *requestor, int instance)
 {
   if (nrequest == maxrequest) {
     maxrequest += RQDELTA;
@@ -919,6 +919,7 @@ int Neighbor::request(void *requestor)
 
   requests[nrequest] = new NeighRequest(lmp);
   requests[nrequest]->requestor = requestor;
+  requests[nrequest]->requestor_instance = instance;
   nrequest++;
   return nrequest-1;
 }
diff --git a/src/neighbor.h b/src/neighbor.h
index 51add41c1b..8c90569dfd 100644
--- a/src/neighbor.h
+++ b/src/neighbor.h
@@ -71,7 +71,7 @@ class Neighbor : protected Pointers {
   Neighbor(class LAMMPS *);
   virtual ~Neighbor();
   virtual void init();
-  int request(void *);              // another class requests a neighbor list
+  int request(void *, int instance=0);  // another class requests a neigh list
   void print_lists_of_lists();      // debug print out
   int decide();                     // decide whether to build or not
   virtual int check_distance();     // check max distance moved since last build
diff --git a/src/pair.cpp b/src/pair.cpp
index f3986a3b1f..42ad10032b 100644
--- a/src/pair.cpp
+++ b/src/pair.cpp
@@ -44,10 +44,16 @@ using namespace LAMMPS_NS;
 
 enum{NONE,RLINEAR,RSQ,BMP};
 
+// allocate space for static class instance variable and initialize it
+
+int Pair::instance_total = 0;
+
 /* ---------------------------------------------------------------------- */
 
 Pair::Pair(LAMMPS *lmp) : Pointers(lmp)
 {
+  instance_me = instance_total++;
+
   THIRD = 1.0/3.0;
 
   eng_vdwl = eng_coul = 0.0;
@@ -70,7 +76,7 @@ Pair::Pair(LAMMPS *lmp) : Pointers(lmp)
   ewaldflag = pppmflag = msmflag = dispersionflag = tip4pflag = dipoleflag = 0;
   reinitflag = 1;
 
-  // pair_modify settings
+  // pair_modify settingsx
 
   compute_flag = 1;
   manybody_flag = 0;
@@ -246,7 +252,6 @@ void Pair::reinit()
   if (!reinitflag)
     error->all(FLERR,"Fix adapt interface to this pair style not supported");
 
-
   etail = ptail = 0.0;
 
   for (int i = 1; i <= atom->ntypes; i++)
@@ -273,7 +278,7 @@ void Pair::reinit()
 
 void Pair::init_style()
 {
-  neighbor->request(this);
+  neighbor->request(this,instance_me);
 }
 
 /* ----------------------------------------------------------------------
diff --git a/src/pair.h b/src/pair.h
index a29186ff4c..d58b79de9d 100644
--- a/src/pair.h
+++ b/src/pair.h
@@ -30,6 +30,8 @@ class Pair : protected Pointers {
   friend class ThrOMP;
 
  public:
+  static int instance_total;     // # of Pair classes ever instantiated
+
   double eng_vdwl,eng_coul;      // accumulated energies
   double virial[6];              // accumulated virial
   double *eatom,**vatom;         // accumulated per-atom energy/virial
@@ -182,6 +184,8 @@ class Pair : protected Pointers {
   virtual unsigned int data_mask_ext() {return datamask_ext;}
 
  protected:
+  int instance_me;        // which Pair class instantiation I am
+
   enum{GEOMETRIC,ARITHMETIC,SIXTHPOWER};   // mixing options
 
   int special_lj[4];           // copied from force->special_lj for Kokkos
diff --git a/src/pair_hybrid.cpp b/src/pair_hybrid.cpp
index 3c7a51633a..e24f9788ee 100644
--- a/src/pair_hybrid.cpp
+++ b/src/pair_hybrid.cpp
@@ -431,7 +431,7 @@ void PairHybrid::init_style()
   for (i = 0; i < neighbor->nrequest; i++) {
     if (!neighbor->requests[i]->pair) continue;
 
-    // istyle = associated sub-style
+    // istyle = associated sub-style for that request
 
     for (istyle = 0; istyle < nstyles; istyle++)
       if (styles[istyle] == neighbor->requests[i]->requestor) break;
@@ -582,7 +582,7 @@ void PairHybrid::modify_requests()
 
     if (j < neighbor->nrequest) irq->otherlist = j;
     else {
-      int newrequest = neighbor->request(this);
+      int newrequest = neighbor->request(this,instance_me);
       neighbor->requests[newrequest]->copy_request(irq);
       irq->otherlist = newrequest;
     }
@@ -725,7 +725,7 @@ void PairHybrid::modify_params(int narg, char **arg)
         if (strcmp(arg[1],keywords[m]) == 0 && multiflag == multiple[m]) break;
       if (m == nstyles) 
         error->all(FLERR,"Unknown pair_modify hybrid sub-style");
-      Pair::modify_params(narg-2,&arg[3]);
+      Pair::modify_params(narg-3,&arg[3]);
       styles[m]->modify_params(narg-3,&arg[3]);
     }
     
diff --git a/src/pair_lj_cut.cpp b/src/pair_lj_cut.cpp
index 8e4219c53d..8426862e04 100644
--- a/src/pair_lj_cut.cpp
+++ b/src/pair_lj_cut.cpp
@@ -490,32 +490,32 @@ void PairLJCut::init_style()
     if (((Respa *) update->integrate)->level_inner >= 0) respa = 1;
     if (((Respa *) update->integrate)->level_middle >= 0) respa = 2;
 
-    if (respa == 0) irequest = neighbor->request(this);
+    if (respa == 0) irequest = neighbor->request(this,instance_me);
     else if (respa == 1) {
-      irequest = neighbor->request(this);
+      irequest = neighbor->request(this,instance_me);
       neighbor->requests[irequest]->id = 1;
       neighbor->requests[irequest]->half = 0;
       neighbor->requests[irequest]->respainner = 1;
-      irequest = neighbor->request(this);
+      irequest = neighbor->request(this,instance_me);
       neighbor->requests[irequest]->id = 3;
       neighbor->requests[irequest]->half = 0;
       neighbor->requests[irequest]->respaouter = 1;
     } else {
-      irequest = neighbor->request(this);
+      irequest = neighbor->request(this,instance_me);
       neighbor->requests[irequest]->id = 1;
       neighbor->requests[irequest]->half = 0;
       neighbor->requests[irequest]->respainner = 1;
-      irequest = neighbor->request(this);
+      irequest = neighbor->request(this,instance_me);
       neighbor->requests[irequest]->id = 2;
       neighbor->requests[irequest]->half = 0;
       neighbor->requests[irequest]->respamiddle = 1;
-      irequest = neighbor->request(this);
+      irequest = neighbor->request(this,instance_me);
       neighbor->requests[irequest]->id = 3;
       neighbor->requests[irequest]->half = 0;
       neighbor->requests[irequest]->respaouter = 1;
     }
 
-  } else irequest = neighbor->request(this);
+  } else irequest = neighbor->request(this,instance_me);
 
   // set rRESPA cutoffs