Importing E-M5 RAW-files into Apple Aperture
after starting the thread, I tried to search for an answer for the 934th time, and this time I found the solution. It had indeed something to do with the preview settings.
Just go to the Aperture settings > Import Settings > Standard Preview (instead of that other option, I can't remember since I'm at work right now).
Next time you import new RAW-files, it will not have that problem. Still think it's strange since I didn't have that problem with my GF2 RAW-files.