Looks like the changes of bug 403929 haven't been made to the overlay yet. Results in broken dependencies if you have the overlay added.
To my knowledge, the multimedia-overlay is not official and not handled by the Gentoo's bugzilla. Should propably contact the overlay maintainers directly.
Unless something changed while I was away, the multimedia overlay *is* official, and should be handled by Gentoo's bugzilla. Therefore reopening.
This has been fixed