The bug
If you are pushing space and shift in spectator or creative mode while you are in water, you start swimming up like in survival mode instead of staying at your current position like it is the case if you do the same while not in water.
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if you are pushing space and shift with this mode in water, player interact like creative or survival mode. try it!!

I still don't get it.
Please attach screenshots.
okay... I'm interacting with water, and water push me up
It's not the same bug that https://bugs.mojang.com/browse/MC-46470 , Dinnerbone only fix the sound and particles of water but I can float in the water while I press the shift and space... it's uncomfortable to move in it...
And yes, is in the 14w31a

Confirmed for:
Minecraft 1.8-pre 2 _When you press SHIFT and SPACE while beeing in water you fly until the surface and then you stop (like Pablo González Rubio said)
To clarify the report: When in creative or spectator mode, if you press both the fly and crouch keys while in water or lava, you will move upwards. This is because swimming is still enabled, and overrides the crouch key.

Confirmed for
15w37a

Confirmed for
16w05b
This issue relates to MC-46417.

Confirmed for 17w14a

Changed the report to include Creative mode as well since at least one of the tickets closed as duplicate of this report was only about Creative mode.
Can you please go a little bit more in detail, how can you interact with water then?
When you mean the particles, yes I can confirm that