I just finished a portrait session where I shot 4 sheets of precious E100 in fading light so I was working fast. I realized when I got back I may have had the back oriented upside down (vertical position), so the lip wasn’t locking perhaps??? I noticed I can lock the back into place in either direction but the holders only seem to lock going in one way. However I was working fast so I didn’t notice at the time. I’m sure this would have caused a light leak but of course I can’t run E6 until about a week from now. Ugh I’m just kicking myself because this poor couple posed in incredible light so patiently. Kind of seems like a design flaw that I was able to mount the back this way. I guess some users may want to load the film from the bottom up but still…. Has anyone else done this?