Did it happen when the spool was less full? When the spool nears empty, it has to spin faster to release the right amount of thread. Apparently this builds up some kind of static caused by the friction and makes the bobbin misbehave. My Singer 301 FMQs very well, but the bobbin thread will remove itself from the slot it needs to be in when friction builds up. On my last quilt, I just put in a full bobbin when this would happen and saved the emptier ones for piecing. It's not worth arguing with the machine.
I want to try those little teflon Bobbin Genies. I wonder if my LQS carries them.