You know, I'm not sure we're even supposed to be able to undock the input panel, although it wouldn't make a lot of sense to have that option there. I've actually never even noticed this until reading your message, because after three weeks of using SP2, I don't think I've opened the TIP manually even once. Whenever you need to use the TIP, it just pops up undocked, next to the box you want to type in.
In any case, mine won't undock either if I open the TIP from the task bar. Can't see why you would want to do that in the first place though.