worried about my lens - help

[el.wu]

I seem to have accidentally spinned the front element of my 50mm/1.8 lens backwards (and I don't mean the focus ring) and now compared to the other 50mm/1.8 I happen to have at the moment (it's my friend's) the front element is clearly retracted. That is, when I focus on infinity it doesn't move quite as far forward as the other lens. When I focus at the closest possible distance, the front element goes such a long way backwards that it almost disappears completely.

I have no idea how I managed to do that since I don't remember using force -- I never do that, actually. I tried to put it back in place in a very gentle manner but I couldn't and I didn't want to risk using any more force. Should I be worried about what happened? The lens seems to work fine and focus sharp, but I haven't really done any extensive testing yet.