>Generally for this sort of thing it helps to keep things as bog-standard as possible, and avoid any third party drivers or utilities, or configuration customizations. For example, on Windows hosts I like to use the Microsoft Mouse and Keyboard Center suite so I can remap my mouse's wheel click as a double click. If you have anything like that on either the host or the guest you could test with it disabled.

I keep my windows guest as thin as possible. Luckily it's insubstantial, or else I could be accused of substance abuse :).

>I was going to suggest testing with the guest additions disabled in the Windows guest but that's probably too much of a PITA. AFAIK you can't disable just the mouse additions while leaving the keyboard, video, seamless integration/shared clipboard etc.

Not worth the trouble - the shared clipboard (which works swimmingly in this configuration - I can copy in a linux-to-windows RDP session and paste in windows guest in virtualbox) is a must-have.