In some case, korganizer will show the exact same folder of dav twice in korganizer. When do operation on any of them, both folder will change together, seems to indicate that they are exact same folder and calendar view don't show the contents twice. And such case can survive reboot, akonadi restart. screenshot: http://wstaw.org/m/2013/03/04/plasma-desktopjL1212.png Reproducible: Sometimes
might be specific to the CardDav Akonadi resource, so reassigning there.
I've fixed this yesterday in 4.10