valgrind question

[Boyce Griffith]

Hi, Folks --

I am trying to track down a bug in some of my code using Valgrind 3.4.0. 
  I'm using OpenMPI 1.3, which directly integrates with Valgrind. 
Unfortunately, I have not completed the process of transitioning my code 
from PETSc 2.3.3 to 3.0.0, so these runs are using PETSc 2.3.3-p15.

Running my code with Valgrind, I get a number of errors like the following:

Invalid read of size 8
    at 0x6104C8F: UnPack_1 (vpscat.c:421)
    by 0x61047A4: VecScatterEnd_1 (vpscat.h:150)
    by 0x6133B2B: VecScatterEnd (vscat.c:1564)
    by 0xC6A258: IBTK::LDataManager::endDataRedistribution(int, int) 
(LDataManager.C:1200)
    by 0xA0AEF2: 
IBAMR::IBStaggeredHierarchyIntegrator::regridHierarchy() 
(IBStaggeredHierarchyIntegrator.C:1196)
    by 0xA0CF53: 
IBAMR::IBStaggeredHierarchyIntegrator::advanceHierarchy(double) 
(IBStaggeredHierarchyIntegrator.C:653)
    by 0x7308C4: main (main.C:798)
  Address 0xa66bfd0 is 496 bytes inside a block of size 528 alloc'd
    at 0x4A05FBB: malloc (vg_replace_malloc.c:207)
    by 0x63DCFAF: PetscMallocAlign (mal.c:40)
    by 0x63EA8A0: PetscTrMallocDefault (mtr.c:194)
    by 0x611BDB2: VecScatterCreate_PtoS (vpscat.c:1570)
    by 0x6121252: VecScatterCreate_StoP (vpscat.c:1946)
    by 0x6122D2D: VecScatterCreate_PtoP (vpscat.c:2123)
    by 0x6131B08: VecScatterCreate (vscat.c:1380)
    by 0xC6960F: IBTK::LDataManager::endDataRedistribution(int, int) 
(LDataManager.C:1158)
    by 0xA0AEF2: 
IBAMR::IBStaggeredHierarchyIntegrator::regridHierarchy() 
(IBStaggeredHierarchyIntegrator.C:1196)
    by 0xA0CF53: 
IBAMR::IBStaggeredHierarchyIntegrator::advanceHierarchy(double) 
(IBStaggeredHierarchyIntegrator.C:653)
    by 0x7308C4: main (main.C:798)

Has anyone seen this kind of error crop up before?  Does it indicate 
that I am messing up the call to VecScatterCreate?  (This VecScatter is 
being used to scatter data between ghosted Vecs, and I wouldn't be 
shocked if I have made a dumb mistake.)  Could Valgrind be returning a 
false positive?

Again, this is with PETSc 2.3.3-p15.  I am working on getting things up 
and running with PETSc 3.0.0.

Thanks!

-- Boyce