I believe that before the SU10 Beta it was possible to apply a material to an Apron or Painted Line just by leaving the material selected and then pressing the material button on the object, which was much easier for Painted Lines where we spent a lot of time applying the same material to various objects. Now that doesn't happen anymore, I have to drag and drop the material over a small field on the object and this slows down a lot the development of large airports with many lines. From the description of the tooltip this doesn't seem to be a bug, but I wish it were possible again.