[CLIENT] Masteries Drop Down Scroller Forcibly Closes

1. Go into champ select screen
2. Click on masteries to open the drop down list
3. Attempt to scroll down using the side scroller
4. It closes

This happens every single time I am in champ select. It seems as if the bug has been present for years now. For the scroller to actually work, you have to open the drop down list multiple times and just hope it works. This is a problem because my mouse scroll button is broken. Thank you for your time