Try folding the paper on the preforation made by the seam and running your fingernail along the crease of the fold prior to tearing. I have found this gets it to release much better. You may also wish to decrease your stitch length even more. You want it to be really small. I am talking small that if you go to unsew it is a complete and utter pain in the patoot. Your stitching should not be coming undone that easily, even with copier paper.