Scroll bar between roster and options sometimes bugs out (40k and WHFB)

[Dr. Cheesesteak]

Sometimes while I'm making a roster for either Warhammer 40k or Warhammer Fantasy Battle, the scroll bar bugs out.

What happens is something like this: I click on a unit and then mouse over to the options. Somehow the scroll bar catches the mouse (w/o me ever clicking anything) and moves as the mouse moves. So basically, when I click a unit and move the mouse over to the options section, the scroll bar just starts scrolling up or down and also highlights another separate unit.

This is very frustrating and annoying. Has anyone else experienced this?