There is a small pin at the base of the window that is supposed to keep the window from jumping out of the track. This pin rides up and down inside of the track behind the weather strip. Check the lower mount for the window track to see if it is loose, that will cause the pin to come out and jump the track, as will a broken pin or worn out track. Be careful working on the window as the vert vindows are unique to the convertible and are hard to find anyplace. You hinge pins, if badly worn, can also cause problems with the window as excessive play in the pins can shock the window and track when road bumps and pot holes are encountered.
Dave