Last week while out shooting for 620 camera day, I had an odd failure which had never seen before. I was using my Meteor, with a piece of black electrical tape over the red window, as is my practice with this style of camera in order to reduce the chance of light leaks. Somewhere in the middle of the roll, as I was advancing the film and peeling back the tape to observe the numbers, I noticed that the red window had vanished! It was quite disconcerting looking into the back of the camera and seeing the numbers so crystal clear, unencumbered by the piece of red plastic. For the rest of the roll, I was as careful as I could be to shield the opening from the light as I was advancing. But the film (Portra 400) has not come back from the developer yet, so I still don't know how much of a light leak problem this actually incurred.
My initial thought was that the window either fell off and onto the ground somewhere, or else had somehow been pushed into the camera. But when I got home I discovered what had actually happened - it had been pulled off by the electrical tape, and was still stuck to it!