Major GL-2 problem, lets see if you experts can explain this

my school has two GL-2's that a there for students to check out and use for projects, so these are well used Canons and have had alot of useage. We have had some of the same problems everyone else has with Canon's, the rewind problem, the recording lines of all still video on your footage you shot. But yesterday we found a new one.

A student brought in footage and said he had something strange happen, while he was shotting, a 5 sceond video image popped up on the Canon and recorded on to a tape that was blank, with footage that was from a week before in class when we were shoting useing a different tape. The sound was perfect the image was perfect it looked as if it was recorded from the tape that had the oringle shot on it. What i don't get is what in the Canon GL-2 would hold the same great looking picture in the Canon and record it on a new blank tape when you are recording something else. I mean we know these GL-2 are done for and we need new ones but how could this happen?