When I was creating my Cookie Clicker redstone contraption, I came into a bug.

Whenever you place a piston, sticky or non-sticky, at Y=0 and power it, it does not push. In the image it shows two pistons: one at bedrock and the other one layer above bedrock. The piston a layer above bedrock is powered and pushes, while the piston that is powered (also in my T-Flip Flop) that is in the bedrock layer doesn’t.

I tested this out in 1.6.2 and it produced the same results.