having the same issue with Quantum jump and jetpack not working with Forge 4.1.4.275
I'm pretty sure the forge version has nothing to do with it really, I think its more to do with ic2 itself.
Then again I could be wrong and this all could be a problem with player hooks in forge for multiplayer.
But I don't see changing the forge version helping much, other than its good to have the latest version.
Speaking of latest versions It may be worth noting that I redownloaded ic2 1.106 and found that the file size of the ic2 jar had grown from 7,333kb to 7,342kb since the day of release and there's no version number change at all.
So yeah look out for those ninja updates