Found this on a KDE forum. If you copy ~/.gtkrc-2.0-kde created by gtk-engines-qt over to ~/.kde4.0/share/config/gtkrc-2.0, you will have a working gtk-qt theme engine in KDE4. The default installation of gtk-engines-qt only works in KDE3.x.
Steps to Reproduce:
1. Install KDE4
2. Install gtk-engines-qt
Same as 'cp ~/.gtkrc-2.0-kde ~/.kde4.0/share/config/gtkrc-2.0'
Not maintained by KDE...
and how shall I fix that in the ebuild? I think this bug belongs to upstream for changing the path in their application - please report it there.