Nancy Moore

Oh boy, let's see if I can explain this. The lining in the jacket is most likely "bagged" which is a ready to wear technique. This technique involves only pressing (not sewing) the sleeve hem and jacket hem up, preparing the lining and leaving 8-10 inches open in one of the sleeve linings (either one), then sewing the lining into the jacket the traditional way (stitching to within about 5-6" inches of the bottom on either side), The garment is turned inside out through the sleeve lining opening and the garment and sleeve hems are attached to the lining. When turned back into place the lining holds the sleeve and garment hem up and in place. The opening in the lining is then closed by sort of topstitching the opening closed. This actually works **most** of the time. You can easily check to see if this technique was used by turning the sleeves inside out and looking for the place in the sleeve lining when it was closed by topstitching.  OK - now the difficult part, explaining how to do this...

Pick out the "topstitching" that closed the lining sleeve. Well above your alteration, pin the lining and sleeve together so it doesn't twist when you pull it through. Reach through the sleeve lining opening grasp the bottom edge of the sleeve and pull it through the opening. You'll need to unpick the stitches of the present hem. Make your alteration to shorten the sleeve and lining (assuming you have to cut it), be sure to maintain the same ratio of lining length to sleeve length or the lining will pull when you put it back. Right sides together, stitch the sleeve hem to the lining. Turn inside out, press, then close up the lining seam opening by topstitching again.

This may have not been clear, it's one of those things you may have to see to understand - Threads had an article on this sometime back, and also you can reference Claire Shaffer's Rodale Press "High Fashion Sewing Secrets" book. Should be available at the bookstore.