So I wrote a big email about this mysterious message I was getting, but then after some research and poking and debugging tracked it down to a dangling pointer in C that was causing a callback to point to an invalid address, which somehow worked anyway 99% of the time. That all said, I'm not totally convinced that "freeHaskellFunctionPtr: not for me, guv! 0x23143f0" is the clearest error message ever. Now, if it were in a more contemporary American idiom such as "wtf this ptr ain't from MY house lol!!!" I probably would have found the bug in half the time. Anyway, I fixed my bug and I'm happy about that, but I didn't want to waste a chance to send an email with this title...