diff -r 7f0211769daf src/vec/vec/impls/mpi/pmap.c
--- a/src/vec/vec/impls/mpi/pmap.c	Wed Mar 28 13:34:25 2012 -0500
+++ b/src/vec/vec/impls/mpi/pmap.c	Fri Mar 30 18:59:22 2012 +0300
@@ -188,6 +188,8 @@
   ierr = PetscMemcpy(*out,in,sizeof(struct _n_PetscLayout));CHKERRQ(ierr);
   ierr = PetscMalloc((size+1)*sizeof(PetscInt),&(*out)->range);CHKERRQ(ierr);
   ierr = PetscMemcpy((*out)->range,in->range,(size+1)*sizeof(PetscInt));CHKERRQ(ierr);
+  if (in->mapping)  {ierr = PetscObjectReference((PetscObject)in->mapping);CHKERRQ(ierr);}
+  if (in->bmapping) {ierr = PetscObjectReference((PetscObject)in->bmapping);CHKERRQ(ierr);}
   (*out)->refcnt = 0;
   PetscFunctionReturn(0);
 }
diff -r 7f0211769daf src/vec/vec/interface/vector.c
--- a/src/vec/vec/interface/vector.c	Wed Mar 28 13:34:25 2012 -0500
+++ b/src/vec/vec/interface/vector.c	Fri Mar 30 18:59:22 2012 +0300
@@ -1487,6 +1487,7 @@
 @*/
 PetscErrorCode  VecSetBlockSize(Vec v,PetscInt bs)
 {
+  PetscErrorCode ierr;
   PetscFunctionBegin;
   PetscValidHeaderSpecific(v,VEC_CLASSID,1);
   if (bs <= 0) bs = 1;
@@ -1496,7 +1497,16 @@
    Try setting blocksize before setting the vector type",v->map->n,bs);
   PetscValidLogicalCollectiveInt(v,bs,2);  
 
-  v->map->bs   = bs;
+  if (v->map->refcnt > 0) {
+    PetscLayout map = PETSC_NULL;
+    ierr = PetscLayoutCopy(v->map,&map);CHKERRQ(ierr);
+    ierr = PetscLayoutDestroy(&v->map);CHKERRQ(ierr);
+    v->map = map;
+  }
+  if (v->map->bmapping) {
+    ierr = ISLocalToGlobalMappingDestroy(&v->map->bmapping);CHKERRQ(ierr);
+  }
+  v->map->bs = bs;
   v->bstash.bs = bs; /* use the same blocksize for the vec's block-stash */
   PetscFunctionReturn(0);
 }