jlehmus My dear Russian camera user/collector.- At first wellcome.- Your camera is deffective. I regret to say. I used all FED camera series and never ocurred such problem. Normally FED (2 onwards) cameras has two latches in the bottom. The one in the film cassette position has a "C" shaped lamelar spring. This spring is secured by a single middle screw. This compensing spring is used to mantain the cassete against the upper camera wall during all the winding process. When this spring is broken or removed, ocurs the related problem. But this is not a serious problem; If you can count in your own skils (or from any one) you can do a small spring to fix the problem. LP
Minute variations in the camera's part's specifications will account for this. And it's not only in FED-2 or -3 that this happens. I've seen this happen in almost all of my III-series Leicas, some of my FED-1 and Zorki-1, and even with my Praktica SLRs as well. I don't find them offensive at all- in fact, I often like the effect, the sort of "charming characteristic" you mentioned in your blogsite.
There are tricks and remedies available to relieve this slight frame to gate misalignment. But most of these involve clumsy modifications like using spirals under the cassette and takeup to push these up.
And with transparencies/slides, I must say that I've never had a problem with them too. Most of the slide frames have really smaller windows compared to the actual frame size on the film. The slight misalignment is often hidden under the frame.