I'd like to have mouse wheel support enabled for comboboxes, so I removed the #if in ComboBox::mouseWheelMove (By the way, I'd love to see a method added to enable the mouse wheel instead of using a #if). Now it works, but the only problem is that for every click of the wheel the ComboBox increments by two. I confirmed on both Mac and Windows, and I'm using the latest Juce code.
Interestingly the problem does not occur if I hover over the up/down arrows of the combo box, and only occurs when hovering over the text label. This is due to the text label having a mouse listener. If I comment out the mouse listener then the scrollwheel increments properly, but then the popup box doesn't popup anymore.
Based on these threads, it looks like others have hit this problem.