Hmm. That's a super weird signal to crash on in that function. It's when you call a system function with a bad argument. I couldn't reproduce the error. Can you give me any more information? Which Chipmunk/Xcode/SDK versions? Can you make a project that replicates the issue as simply as possible that you can send me?
So leafSetTrans() may have some other function calls into it which may call calloc(). There is also an assertion to check if the allocation worked correctly that may call cpMessage() which can call printf() and friends. So something with a failed allocation is the best I can think of for what is causing the SIGSYS.