I've not seen anything like this. With that out of the way, here are the places I would look for information.
- Before doing anything else, check your Xorg log (you'll find the most recent two in /var/log/). There may be an indication of a problem in the messages therein.
- Check your dmesg(8). The mouse may be vanilla, but the interface or controller might not. Use that information with #3.
- Check the misc@ archives, using the mouse and controller drivers from your dmesg. There's nothing in misc@ that matches your "scroll wheel" issue closely, though there was someone with a similar problem with a KVM mouse that turned out to be hardware; it just manifested itself at the time of an upgrade.