Wee... after a helluva lot of guesswork and eventually giving up and
staring not just at the spec but at a disassembly of PXE code in memory,
I think I have a recipe that allows at least Intel PXE 2-derived PXE
stacks to be cleanly unloaded from memory.
Please try it out...
http://www.kernel.org/pub/linux/utils/boot/syslinux/Testing/
This is *basically* a 1.75 release candidate, although there is some
debugging code I want to remove first.
-hpa