One of Mp3tag's biggest user interface problems is with fields that are both user-editable text and selectable from a drop-down list. Wheel mice pose a problem. I cannot count how many hundreds of times I've been editing some complex expression in a filter or in a converter and lost the edit due to the mouse wheel moving, causing the text to be overwritten from the drop-down.
How about this?
When a user begins editing a field, disable the ability to use the mouse wheel to select from the drop-down. If the user wishes to abandon the edit and use the wheel, then can either 1) click the down-arrow, re-activating the drop-down, 2) use keyboard up/down navigation keys to re-activate it. In both cases, allow the wheel to be used again until the user begins editing in the text box.