1st check that the motherboard is at current firmware/BIOS level. If it still does it, then I'd say you are in the component builder's idea of hell. Both mobo and CPU vendor can point fingers at one another and you're going to be sitting in Tech Support purgatory.
My best guess it is a CPU issue, but I can't swear to it.
Realistically, if this ever happens to me I'd say "fsck it all" and send both mobo and CPU back.