This circuit used to be 1 tick in 1.4.6 and it would let go of a block with a sticky piston and no longer does, i dont know if that was a bug thats been fix but I've used it to control clocks.
Circuit Img#1 to let go of the black wool block
It did not let go of the block (tested N S and W E)
Build circuit Img#1 in 1.4.6 and the piston will let go, then build it in the snapshot it will not
Circuit 2 acts just like circuit 1 did before the snapshot and it no longer does after the snapshot
Circuit Img#1 - Broken Circuit (Repeater set to 3 ticks)
Circuit Img#2 - New Working Circuit