The dropdown List UI control has a way of interacting with a mouse over event in which, if the mousewheel is used over this control, the control then flips between the items in the list. This sounds helpful in theory, however there is a common use case that makes this a problem.
The mouse wheel is ALSO used to scroll up and down a long rollout. The most common example is the Edit Poly rollout, where, unless you expand the control panel to three columns, it's impossible to work without continuously scrolling up and down hunting for buttons.
Now, while you scroll up and down using mouse wheel, because the scroll bar is tiny and barely visible, the cursor is bound to go over the "Select By Name" dropdown list in the "Polygon: Material IDs" panel. at which point, the rollover scrolling stops, and the mousewheel instead flips between names selections, changing whatever existing selection there was until now. The user then has to stop, undo, and slowly navigate around this control to avoid invoking it again.
This happens to me very often, to the point of annoyance.
My suggestion is to change the way a dropdown interacts with a mouswheel even so that ONLY mousewheel events that were initiated when the cursor was already over the control would be interpreted as flipping between items.
Additionally, you might consider having the mousewheel scroll up and down rollouts when it's over the scrollbar.
