One last point on VirtualBox; it has (in the past) returned faulty register values causing bugs to appear in OpenBSD guests ... I don't recall seeing any reparations published for the particular flaw cited in the misc@ thread below.
ershiba and other Virtualbox users should keep it in mind if operational errors occur in VB guests:
http://marc.info/?l=openbsd-misc&m=120492689515501&w=2