First off, I'm not sure what to call this piece of the window frame. It's the top horizontal bar that you use to pull the window up and latch to the little tabs.
Anyway, mine came off when I opened it. First the corner came up just as it was being latched than the rest detached so now the window is fully closed with nothing to grip for opening. The frame piece does not appear to have been attached with any adhesive.
Today I'm going to see if I can get it open and reattach the thing but I would be interested if anyone else has had this issue any what was done for a fix.