Put simply, retracting multiple sticky pistons in a row used to be able to pull each other back, assuming the one being pulled isn't extended.

After some testing, the sticky piston being retracted will grab only the block connected to it, and if that block being pulled is another sticky piston, it won't drag the next block back.

Here's the end result---

This is a video I made to further demonstrate the problem---

http://www.youtube.com/watch?v=awPDkvNFwTo