virtualbox.org

No idea. You did already install the Guest Additions? Perhaps that is needed in your case. However, I've seen another user that had this problem with his many buttons mouse, as where a normal 3 button mouse with scroll wheel worked without problems.

Yes, GA installed and working (minus shared folders off course ).
Well, will try with another mouse, and see what happens. Looks like Vbox does "not like" MS mouse.