Just to provide a quick recap for any who follow this thread...

The problem came from a locally compiled version of afni,
compiled with gcc 4.2 on the 10.5 Intel mac. The distributed
binaries are built on 4.2.1, and fortunately do not show this
bad behaviour.

Key point: the distributed binaries seem okay.

On occasion, we need to alter the compile optimization flags
when compiled code mis-behaves. It is important to watch out
for these types of issues, because if we are stuck with a
certain compiler for some system, then all we can do is play
with the flags.

So for any who compile macosx_10.5_Intel, avoid compiler
version 4.2. Upgrade to 4.2.1.

- rick