On how to fix, maybe trying sudo make uninstall in build dir, then something like
sudo rm /usr/bin/amarok
sudo rm /usr/local/bin/amarok
sudo rm `which amarok`
and then trying compiling again with clean build dir, mkdir amarok-build-new && cd amarok-build-new && cmake ../amarok -DCMAKE_INSTALL_PREFIX=`kf5-config --prefix` && make && sudo make install could do the trick