Linux (current build as of 16 Apr 2019)

Reproduction:

Be in full screen mode
Enable spectator_window via console (spectator_window true)
Attempt to disable spectator (spectator_window toggle, or spectator_window false, or spectator_window off).

Expected result:

Spectator window closes.

Actual result:

Console says "spectator_window off", but 2nd window remains open.