I had this issue, with help from #debian-kde in irc.debian.org fixed it by installing libkdecore5 from sid manually (aptitude throws a lot of dependencies and attempts to uninstall most of programs).
So, that's my advice, download libkdecore5 .deb from sid and dpkg -i it -- To UNSUBSCRIBE, email to debian-qt-kde-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/201006131840.33638.micr...@ei.upv.es
