There are several issues, Theo has posted a lengthily mail about VirtualBox trashing registers in userland causing subtle bugs.
http://marc.info/?l=openbsd-misc&m=120492689515501&w=2
It's still not a bright idea to use virtualization in a production environment, it's disgusting how many people do that these days.
Just use real hardware, not pseudo-hardware with a boat load of potential emulation bugs.. it's real simple.