Asserts due to clobbered free memory

[Mike Alexander]

I'm getting crashes in GnuCash with an error like

gnucash(59868,0x7fff7e813180) malloc: *** error for object 
0x7f950b29e008: incorrect checksum for freed object - object was 
probably modified after being freed.

I'm running the X11 version on MacOSX 10.8.5 and I just updated to the 
current head version.  I have been getting these for a while and was 
hoping that updating would make them go away, but I just got another 
one.  Has anyone else seen this?  I'm running an optimized version of 
GnuCash so I'm sort of surprised that malloc is making these checks. 
One "solution" would be to figure out how to turn it off, but I suspect 
there is a real problem here somewhere.

           Mike