I have noticed that when my right mouse button is held down, which is practically always during combat, my mouse wheel does not zoom.
I suppose this should really be a bug report, however, it would be nice if when while the right mouse button was being held down the mouse wheel could select next/previous enemy.
If I hold down the right mouse button and do not move the camera the wheel will zoom, only after I have moved the camera does the zoom function stop working.
Perhaps an option via the UI could be added for this feature?