I can confirm this problem. My temporary workaround was to install phonon-backend-vlc start `kcmshell4 phonon`, go through backend and switch it to vlc (move it as top entry). Trying it through systemsettings -> Multimedia didn't work because it froze with a similar problem as amarok. Removing gstreamer1.0 doesn't seem to be possible for me because I would have to remove essentially my whole system
The new release, 4.8, is working correctly. Cheers Sylvain