Hello, found this thread as I am having the same issue as the thread starter. The solution arrived at by other posters which seems to involve restitching of the spring tensioner seems to correspond to another problem later posted but probably not the initial photo. My issue which looks like the issue initially posted seems to be that there is TOO much tension pulling the fabric out of the trim, not that there is too much slack. Please see below

 

I can't post a pic because I've got the hardtop on (and it's raining and dark here anyway), but to fix my stretched cable until I replace it, I loosened the torx screw (i've seen a lot of references to a rivet, but if they're talking about the same thing mine is screw) at the back that holds the cable taut. Then I rotated the eyelet towards the back of the car to put more tension on the cable, and tightened in place. that was enough of a change in tension to fix the problem. It's been about a year and half without the edge of the roof popping out of line again.

 

Thanks for that idea. Just gave it a go and loosened, then tightened the torx screw holding down the cable on the bottom and it didn't lead to any change. I suppose it may be loose from the top screw underneath the trim, although I gotta say the cable doesn't seem to have much slack on it.

 

I guess I got lucky! With any luck, that video from Alan will help.