All files are in 50fps, and the sequence was auto matched (and is confirmed) at 50fps. Accross the entire timeline, each tap of a sideways arrow key changes the preview frame once. However, on some files, I have to scrub to the right two frames to actually see a change. This is as if the file itself was 25fps on a 50fps sequence, but I can confirm the files (according to PP AND Windows) are 50fps.
Why?