When flying through water in spectator mode, the splashing sound still plays. I presume this is because water is the only block with a sound for going through it, because lava doesn't have a sound for this.
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Confirmed the following:
In Spectator Mode you will get a splash, but only for yourself (I used 2 different accounts on lan 1 in spectator mode the second one in all 4 different modes)
Second account picks up:
GM0,1,2 No practiles and sounds
GM3 Practiles and sounds
Only if you should not be abled to see practiles from other spectators in gm3 it would a bug for gamemode 3.
Futher there is no bug in else gamemodes

Confirmed.

Just found this bug in 14w07a ...
Noticed this in 14w29b.
Does this also play for other players?