My Singer will do that when I FMQ meandering from time to time. Thing is...on the top it looks perfect stitch. The machien makes no sounds that anything is wrong..works just fine..nothing out of the ordinary, nothing to say something is wrong. Then when I finish and turn over to cut thread ends....lord have mercy.. the whole area I did is nothing but the thread nests! I can fix it if I adjust the thread tension but still...why would the machine not say something is wrong? The thing bleeps loudly if you tap the foot peddle and the pressure foot is not down. It bleeps loudly if the needle is not threaded. It beeps when turned on or off. But.. when this tension is like this.. not a sound AND when the bobbin thread goes out...it doesnt' beep. I have sewed all over before I noticed the bobbin thread was gone! I mean.. we look at what it is doing as it goes through and before, but I dont' know about you but I dont look at it after it passes through the needle/pressure foot... until I am done with the seam or technique!