Wait so are you just updating it for him or something?
If so I would recommend not as developers are usually working on something when its not out(DUH)
So when he updates his yours will be obsolete and you will get lots of troll comments.
The original author (Hippo) claims that he cant figure out how to update it for 1.4.1. This claim is suspect given the very minor changes made between 1.4 and 1.4.1, that no other mod author has experienced any problems making this transition, and that an arbitrary coder was able to pick up the mod and get it to work for 1.4.1 in only a few days.
In all likelihood Hippo has made a deal with Notch and Jeb to cease all development on pistons-as-a-mod, attempting to freeze the community out while pistons-as-a-feature is hammered out. This sort of strategy will fail precisely because there are over a million users of minecraft. We are legion. There will always be someone to fill the void.
To fix the piston and casing separation bug, maybe try making the two halves craftable into a working piston?
(To fix bug 3 if the Invedit problem is already fixed)
Mediashare says the file is invalid or deleted. Update link?