I have the same issue, I'm on 8.1.39.
Example, north dock has a dropdown for themes. West deck is used for navigation. If the users does something in the west dock, the only way they can use the dropdown in the north dock is to first click the north dock to get focus, otherwise the dropdown "falls" behind.
Note: for me, this is just a test application, so no big deal, but I could see a need down the road and would be nice to at least have a workaround. I couldn't find a way to grab focus programmatically.
Normal (with focus):
Abnormal (no focus):
I think this post is similar?