Weird time-sensitive leaks / problems in the memory manager

Yesterday I saw some leaks with foreach() and custom zend_iterators. Today, the same binary doesn't have those leaks. I had another similar issue a few weeks back on a different machine, but with an overrun reported on shutdown. The next day, the same binary was fine. Unless the linux-fairy visited both those boxes overnight and magically fixed the bugs, I think we have an issue either in the memory manager, or worse, in some other piece of code that is subtly mangling the memory manager headers. (this is with HEAD). Valgrind shows no problems. Looks like it's going to be hours of "fun" trying to track this down. --Wez.