xfce-mcs-plugins-4.2.3 is marked stable on amd64, but it depends on xfce-mcs-manager-4.2.3, which is marked ~amd64.
Not sure why this was changed to enhancement; if xfce4 is installed on an amd64 system, this will cause dependency checking to fail, and block emerge from running.
It seems to be fixed now :-)
yes, this was the result of a failed merge. all fixed up now. xfce4++