Originally Posted by
Peckish
Burying it is not the same thing as tying off. I usually make a quilter's knot, then gently tug the knot through the fabric so it sits in the batting.
You say this is a quilt you made when you were 10. I'm not going to presume what age you are now, but I will suggest that maybe you used cotton thread, and it's old and maybe has rotted? That is not uncommon with cotton thread. If you use polyester thread you won't have that problem.
I'm pretty sure it was polyester thread! It was just one thickness of too-thin normal sewing thread pulled a bit tight and it caught on something, that's all. I can do better than that now by using thicker thread, getting the tension right, using smaller stitches and putting in a knot or a backstitch every now and then. Thanks everyone!