The pictures are self-explanatory, but basically the piston on the right DOES NOT retract after removing a signal, but the one on the left DOES retract after removing a signal. Pictures should be in chronological order from left to right. (This affects snapshots but may or may not affect 1.7.10)

What I expected to happen was: either both pistons to retract or both pistons not to retract.

What actually happened was: one piston retracted and the other didn't.

Steps to Reproduce:
See pictures. Just place that redstone block and then remove it.