I started encountering an error when using kdesu via SSH after Hardy Heron was installed. I’ve since upgraded to 8.04.1 as well and still am running into this bug.
X11 connection rejected because of wrong authentication.
kate: cannot connect to X server localhost:10.0
I know I’m not the only Kubuntu user, and there is proof I am not the only user encountering this error. I’ve been getting around it by using gksu which has no problems with my authentication. I suppose I could just alias kdesu and kdesudo (i tried it with no luck too!) to gksu, but I’d like to see an update fix this in the upcoming months. The nice fade effect of gksu is a welcome change sometimes.