The only two things I can currently think of are:
- Shut down the PC and try inverting the slot your monitors are plugged in in the graphic card
- Right click on the Desktop -> Swap the primary Display -> Apply -> Swap it back
Honestly I'm not sure if it will help but I don't have other ideas aside from purging the configuration, which is probably not the solution and unwarrented.
Another thing to try would be a search on the KDE bugtracker.