Removal of qt3 use-flag from avahi breaks kdnssd-avahi and thus kdelibs:3.5 (both from kde-sunset overlay), if kdelibs is compiled with avahi support. If it is compiled without, it pulls mDNSResponder instead, which in turn blocks avahi; So, if someone (like me) is using kde-sunset overlay, their only options are 1) mask avahi-0.6.25-r1 or 2) remove avahi completely from their system.
Probably INVALID. kde-sunset overlay is by its nature unsupported in the standard portage tree. After all,those packages were officially dropped.
Closing as such. kde-sunset overlay maintainers need to maintain their own copy of avahi for qt3 support, if they want it