|This tip is for older machines with step buttonholes.
My machine has 1(left side, forwards) 2/4 (crossbar) 3(right side, backwards).
When I make buttonholes following the order above, it ends by making the crosstack at the start of the buttonhole. I found that after clipping the threads, my crosstack often unravelled.
Since I find tying off loose threads to be too fiddly for my fat fingers, I get around it another way. After finishing the last crosstack (step 4), turn the dial back to 1 and sew a few stiches down the first side again. The crosstack doesn't unravel anymore after clipping!