Originally Posted by Justin
leftup is 0xfffffebe. WORD_ADDR_XOR is a macro so I can't easily debug what it's returning but maybe it's wrong on 64-bit?

No, I'm pretty sure that leftup is plenty bad enough without having to look at WORD_ADDR_XOR as a culprit. Unfortunately, I don't have a 64-bit machine so that I can take a look myself.