Choose the library tab.
D&D a button to the content panel.
Now click the file tab (so that it gains the panel focus ring).
Hit the tab key and the panel focus ring moves to the layers panel - this is wrong.

When I click a tab I correctly see the panel focus ring appear around it. I therefore expect the tab key to give select the first property in the panel.

To switch to different panels we can use the functionality outlined in: DTL-3453