Hi gang. I'm going to ping @Temechon on this, as well.
Repro:
1. Load simple playground with Window at full-screen (NOT canvas at full-screen. Keep normal 50% split with editor/canvas.)
2. Use settings menu and un-check editor choice (turn OFF editor in settings)
3. Restore the window (de-full-screen it)
4. Drag Window width until it is narrow.
5. Drag Window width until it is wide, again.
Did editor re-appear? It does so in my firefox. Possible PG bugger/oddness. 