FreeBSD as virtualbox guest not working

Hi!
Sometime quite recent a change to FreeBSD CURRENT makes it almost 
impossible to run it as a virtualbox guest, at least under Windows.  If 
I roll back the vbox machine to a (unfortunately quite old, from 
January) CURRENT everything seems to be working.
The issue is that the virtual machine runs very very slow, and makes the 
host almost impossible to work with, especially during compiles and 
other activities involving the CPU and the disk.  I have also 
experienced that the host machine crashes, but that might be unrelated.
Is anyone else experiencing this, or am I doing something very wrong?
Let me know if I need to provide more information or if I can help in 
some other way.
Best Regards!