Pistons take around 3 gameticks to extend. Before the 14w19a update, pistons without a block attached or in front of them, wouldn't cause updates around their arm instantly, but after 3 gameticks. This still works the same way in 14w11b. It seems to occur since the slime block update.

Steps to reproduce:
1 - Build the setup as shown in the picture (with redstone on top of the wool blocks)
2 - Place a redstone torch on top of the redstone block to generate a 1-tick pulse (2 gameticks long).

What should happen or what used to happen:
The bottom piston doesn't extend because it receives an update after 3 gameticks - when its no longer powered.

What actually happens:
The bottom piston extends instantly, at the same time as the other one.

EDIT: The usual update after 1.5 ticks or 3 gameticks also occurs so theres an update at the start and end of the push.

EDIT 06 May 2016:
Fixing this bug would break a huge amount of contraptions at this point and there are no issues with the current behaviour. So resolving this as 'will not fix' would be preferred. Thanks.