I know this thread is old, but their are allot of confusing forum posts about this. I have been experiencing this issue for over 2 years. Apple kindle replace my 13" air after the 2nd repair but the problem is still their.
The Second time apple took my air they replaced a trackpad clip and the battery. (I can't remember or find paperwork for the first)
I am no engineer but I think I know what the problem is. or should I say problems are.
I think its a two fold problem.
First the well know "problem" of the macbook case feeling like its statically charged. I dont know what ill effects this is actually having but it does seem to be causing issues with the trackpad at least.
Second I think the batteries are bulging causing pressure from below the trackpad. This reduces the travel and causes it to be super sensitive.
I think the second issues is the most apparent and most serious.
Maybe soon someone will solve this and maybe apple will use their war chest to offer everyone a free replacement.