In the most recent build of the 8.0.14 nightly,
If you try to have a docked window with any transparency on it (I just mocked this up to show it quickly, but I do have a project design that requires this) then there is a drop shadow on the docked container that I cannot figure out how to remove.
Prior to 8.0.13 there was a bug that added a default white background behind the root container of everything, so you could have any transparency. So I would assume this is related, but that is just a guess.
Applying a box-shadow to the style of the root container doesnt solve this either, however if you do you cant see it in the webpage either.
(Looks same as the image above in the client)