It's gtk2-engines-gtk-qt, most likely. That's still a kubuntu-desktop seed.
You'll need to remove it because it hijacks your Gnome theme. However this is a necessary package to get things like Firefox looking good in KDE, and so should remain in kubuntu-desktop.
If you're installing both -desktop packages, you should be advanced enough to be comfortable removing a package as well.
Maybe we need an autodetection on this to let the user know.
It's gtk2-engines- gtk-qt, most likely. That's still a kubuntu-desktop seed.
You'll need to remove it because it hijacks your Gnome theme. However this is a necessary package to get things like Firefox looking good in KDE, and so should remain in kubuntu-desktop.
If you're installing both -desktop packages, you should be advanced enough to be comfortable removing a package as well.
Maybe we need an autodetection on this to let the user know.