A couple of weeks ago someone posted about having problems with cdburing software. I had the same problem with burning CD's in the KDE too; and I discovered it worked when the KDE was not running (ie. with cdrecord in the command line) If the KDE was running, a lot of scsi command errors appeared, and often the kernel got a panic too when aborting the operation!
I've been able to track the problem to some cdr media watcher service in the KDE, and it seams you cannot shut the damn thing down. This service is added when you install CDBakeOven! After removing CDBakeOven, I was able to burn my cd-roms with K3B again
Hope this info helps some others too with their cd-burning problems.