I had no idea you could assign differing values to MALLOC_CHECK_. I was using 1. I'll have to do some more digging there for future reference.

Yeah, oddly enough the test would complete under valgrind. I haven't seen that before, but I've very rarely tried to use valgrind. I'll check out the options you mention.

I have since resolved the issue and will post the less than flattering details of my debugging above in the hope it may help someone in the future :)