Given your previous problems with K3b+growisofs this might be related to burner+media. But usually growisofs should issue some kind of error message with a little frown in such a case.I doubt this, because it's only happen with DVD+-RWs as for now, but not with DVD-Rs. I also didn't experience this problem when using 5.21. Guess that something was changed from that time which causing this error
I can't reproduce it with DVD+RW... As you maintain that only rewritable media is affected, could you just experiment with command line? I.e. use growisofs with various options from command prompt instead of k3b, *but* complement the line with return code printout, e.g.
growisofs -Z /dev/hdc -R /some/place; echo $? so that the error can be identified. A.