Version:            (using Devel)
OS:                OS X
Installed from:    Compiled sources

Changing memcheck/mc_include.h like this:
 /* We want at least a 16B redzone on client heap blocks for Memcheck */
-#define MC_MALLOC_REDZONE_SZB    16
+#define MC_MALLOC_REDZONE_SZB    64

found interesting stuff.

Methinks the redzone size should be more easily configurable,
ideally with a commandline option.  The current arbitrary
limit of 127 should probably be raised, too.