Steps to reproduce
Create a world (preferrably in creative)
Type /defaultgamemode 0
Quit game and then join again
Observe the world's game mode (either on world selection screen or by going on the world)
It will be the same gamemode as it started off with.
Duplicate of MC-2631, please use the search function to see if your bug has already been submitted. Currently over 57% of tickets are being closed as duplicate.