When you reload a world in 14w26c the setblock clocks stop ,but in 14w21b they are still on no matter what, normally they would still be on, I'm not sure if this is caused by the new way blocks are rendered and stuff, any way the screenshots below.
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@Kumasasa: he means setblock clocks:
command 1
air/redstone_block
command 2
command 1 = setblock ~ ~-1 ~ air
command 2 = setblock ~ ~1 ~ redstone_block
Yeah, what that guy said...
The Clock that runs at 20 ticks/sec
Or just a /setblock ~ ~ ~1 minecraft:redstone_block destroy 0
I think it makes the same bug, not tested yet
What exactly is a "Super Clock" ?