I've done this in Magic Loop when I got confused and started going backwards around the loop. I wasn't actually knitting inside the tube, I'd turned the tube inside out. Sort of. I think it happened when I put the thing down for a while and the yarn got itself between the needles somehow when I picked it back up.
Confirming for me once again that the term "frog" resulted from a cleaned-up version of what you actually want to say as you're ripping out hard-won progress.