Reaper doesn't remember my preferences

[-R-]

First time it happens in more than 3 years, and I think I don't like it at all...
Whenever I change something in my preferences, click apply and ok, Reaper will only remember my preferences until I exit the software. Next time I launch it, all my changes are gone.

It happens with both Reaper 4.78 and 4.75. I'm on windows 8.1.

I tried to import my configuration and import it, I tried to uninstall and reinstall the soft, no luck.

Is there a better way to clean my install?
Any other ideas or experience?

Thanks a lot!

Eric