When placing two sticky pistons on top of one another, and then placing in slime or honey on both pistons, one of the pistons (I found it would be either the top or bottom) will not push but instead get grabbed by the block of slime or honey. I also found that pushing a double and triple piston extender made the same results (this was how I found the bug in the first place).

I was able to replicate the results multiple times.