What I expected to happen was...:
The screen to dock correctly back to windowed fullscreen mode after dragging to the top.

What actually happened was...:
The screen was able to be resized through dragging but the full screen windows button for making the window fullscreen was greyed out and docking was disabled.

Steps to Reproduce:
1. Opened a new single player map to spectator mode on lan
2. Connected with another account
3. Under video settings, turned the game to complete fullscreen.
4. Disabled fullscreen.
5. Attempted to fullscreen through windowed mode.
6. Failure.