When swimming underwater the fly icon on creative will shown even if you are on survival or not, then while underwater and press down the fly icon button you will go more down and when reach it surface you will crouch but the crouch button is hidden and can't you able to go up and can't swim up, so wait for yourself to die before you can go up
Linked issues
is duplicated by 8
3 more links
Still an issue in 1.6.0.1 - the flight controls appear and are functional some of the time underwater. The player no longer gets stuck in the sneak position underwater though.