I have realised that when I have any contents pannel open and my mouse goes over the Traffic++ icon that whatever I had open gets closed. This also deselects the thing that I was placing down (for example a road peice or placing bus stops down). I then have to select the tab again before I can continue. Overlays are also closed if the mouse travels over the Traffic++ icon. I have found that it is specific to Traffic++ icon and have done some playing around trying to break other icons but no others seem to want to break.

This mod is really wonderful otherwise!:)