There's a glitch when using the API to set a player to the GameMode 3.

The player can fly, and can't break blocks. But the noclip function is disable ( Can't go trough blocks ), and the item bar ( wich is rendered on client as I know ), is not showing. If you do /gamemode 3 ( After Exiting This Buggy Mode ), everything works just fine.

The following code can reproduce the error:
(org.bukkit.Player).setGameMode(GameMode.SPECTATOR);