It's very surprising to me, and I'm certain most users, when I press play to start my music player and suddenly evince goes into full screen.  Or when I try to skip a track and suddenly evince jumps in the middle of a page I was reading.  This is totally inappropriate for a PDF viewer!  I understand that you want to make it also able to play in a kind of "presentation mode" but I would argue that this is not among the most common use-cases for a PDF reader, and so this functionality should need to either be manually enabled, or only enabled when in presentation mode.  As it stands now, I don't even see a way to disable it, which is very annoying.