After toasting a few films with the “Canon P” rangefinder I got in Japan earlier this year I ran into problems when trying to scan the negatives: The film gate of the Canon is just ever so slightly larger than those of the Pentaxes I usually use, resulting in a ever so slightly larger area of film exposed to light. This made it impossible to leave a border of unexposed film around the picture in the digital file, which I have grown used to.
The solution is to file out the negative holder of the slide copier I use to digitize my 35mm films. This leaves just enough room around the negatives made with the Canon to form a black border. The negatives from the Pentaxes are not affected by this.
Below an example taken with the Canon P, now with proper black border of unexposed film.