Technically not a bug, but from a user-point-of-view at least an 'unexpected event':
When using the scroll-wheel on a panel that contains drop down menu's (configuration panel, tag editor panel, etc.,) as soon as the location of the cursor happens to touch a drop-down menu entry, the scrolling within the panel immediately stops, and the drop-down menu from that entry opens.
I can't imagine a scenario where that's useful, and I find it quite annoying.
This didn't occur in the past and was introduced sometime last year.
I hope this description is clear enough, if not I can try to create a gif.