If sliding right side back over to right to close window, the left side slips -- and then the right side won't close & allow you to lock the window. You have to push the left side (non-sliding half, no latch) back to the left (due to slipping), in order to get the right side to latch properly. It's tricky, and after a few times, you don't even want to open your windows, because it will take a couple minutes to close them, get the left side to align back into the groove, and the right side (with the latch) to latch properly. These windows don't look old; and I'm told they were six to eight years old. (My 30 year old windows in former place at least would close!) Reason of review: Bad quality.