kubuntu has exactly the same problem as lubuntu with the overlying window border/shadow. It's also very slow without 3D acceleration on, due to kde plasma, not a good choice at all. Remember it has to be a good 2D desktop to work with fusion unity mode. Unity 2D worked great but that's been dropped in 12.10. Ditto gnome classic, also dropped from recent releases.
xubuntu I think I tried a few months ago when I first saw this problem - judging by the fact that I didn't stick with it, and vague memories, I think I can say that it also had the border/shadow problem.
It's the fact that all these different window managers exhibit the same issue that made me comment before about there perhaps being a bug in Fusion's Unity mode.