It my believing that it's not intentional that you can get other gamemodes in debug mode.
The command for "/gamemode <mode>" still actually works. Now I don't know if this is intentional or not, but I suspect not since its locked in the creator but I don't know if thats like default and you can change if you want.
So yh...
Tl;dr disable gamemode command in debug mode.
Comments

Won't Fix
Bugs like this in the Debug World are not being tracked.