Well this is a common issue however don't get stressed here as there are several things to bear in mind.
!st that has definitely jumped out of the runner. The plastic material is a non shattering type and the way to reseat the window is to flex the panel enough to loosen it and re seat it into the channel. The front element is not designed to slide, just the rear! Go on you can really bend them!
2nd If when you have reseated the panels don't be too quick to try and make it slide to easily. loose panels rattle and can often move with vibration. Yes, Yes I hear you say but I can't open the window! Well when sliding the window to another position rather than using brute force that will snap the applied push pad off try flexing the window outwards as you slide it. Think you'll find it now works fine and has two advantages. in that when you have positioned it it will stay there and when closed and parked up it offers quite a difficult operation for a potential thief. He won't think to flex the panel prior to sliding it!
