M3: inter-frame light leakage

[wilt]

I use an M3. Sometimes, light leaks from light-sources close to the image border into the space between frames. This is not a problem, but on really rare occasions, with the sun close to the border, this leakage can penetrate into the next image.

Is this normal behaviour? Why does it happen? I've never encountered the phenomenon on my other camera (OM-2, Hasselblad 500 C, Minox 35).