Theo has already publicly stated that VirtualBox is horribly broken.. it doesn't emulate the x86 properly.
I cannot comprehend why people keep trying to use OpenBSD in a virtual environment.. that's like putting 50 locks on your door while keeping a window wide open.
Just say no, beige boxes will always triumph in dark cold clammy corners.
Reference:
http://marc.info/?l=openbsd-misc&m=120492689515501&w=2
Relevant words of wisdom:
http://marc.info/?l=openbsd-bugs&m=124051336616777&w=2