Steps to reproduce:

1. Open attached project
2. In project tab, select "bugreport.txt" and lock its inspector
3. Maximize any game window (for example, scene)
4. Minimize than window
5. Notice that inspector is unlocked

Additional steps (on 5.3):
6. Lock inspector again
7. Do steps 3-4
8. Notice that this time inspector stays locked

Note: Hierarchy and project tabs don't loose lock state

5.3-only workaround (doesn't work on 5.4): after doing repro steps, lock inspector again. This time maximize-minimize won't mess with lock state.

Reproduced with: 5.2.4f1, 5.3.3p1, 5.4.0b8