2001 S10 Driver's Window Coming Out Of Track

[rdnkcpa]

My son has a 2001 S10 with power windows. The driver's side window came out of the track last week. I took the door panel apart put the window back in the track, put it up and down a dozen times or so to test. All was good, or so I thought. Put it back together sent him on his way. He came home after driving it to work and the window was back out of the track.

 

Can anybody offer and advice on what is causing this? I saw nothing that looked like it was broken or bent.