I have had about a dozen come in with the same problem. First, it is very difficult to over extend the tube as there are build in stops to prevent that with normal extension pressure. I have found that in most cases, the first under cut on a limb was too great and the limb dropped and pinched the bar. The operator then yanks and yanks to try and pull the bar free. The end result is forcing the tube past the built in extension stop. The end result of that is a whole bunch of slides, springs, spacers, etc. in your hands and the outer extension still hanging from the limb. Most can be reassembled with little cost. You must however check for any damage to the tiny bearing cages inside the large guides/spacers and possible damage to the drive shaft, snap rings, etc. Also, attention should be given to the end tube itself with the bar on it. Any dents/scars/bends will require replacement. If there are any kinks in either of the large springs, replace them. If you are unsure where everything goes, go here:
https://www.diyspareparts.com/parts/stihl/diagrams/ht-101/
Good luck and let us know how it went.
OT