[It could be that I should not trim the bobbin thread so close, especially since the back will be covered so no one would see little tails anyway.[/QUOTE]
Good morning, I don't usually post anything but I thought I'd put in my two cents to this. I am new to machine embroidery. I've done kitchen towels, pillows, hats, baby items, t shirts, sweatshirts.
What I've learned through watching many videos.......cut the threads in the back, upper and bobbin, but leave a smidge of a tail. Don't cut so close the knot. Also, people use fray check on these threads as well after cutting them. I have once but don't always.
I've never had a problem with threads coming out at the knot in the back, but I must of cut too close to an actual stitch once and had to hand stitch a tiny section....a pair of baby pants hanging from a clothes line, so it was just a couple of single stitches I had to repair.
I use a Brother Innovis 1250E and love Brother machines, my sewing machine is a Brother as well... They are reasonably priced, user friendly and work horses.