After using the ALT-M feature (Merge vertices),
subsequent transforms give a memory leak:

Error Totblock: 1
maketransverts len: 144 0x86459b4

Create a cube, subsurf, select a face, alt-m-center,
move the resulting vertex, quit.

Also, Subsurf meshes did not get updated correctly
after an ALT-M operation. This seems to have been
magically fixed as a "side-effect" of some other commit.