Both, media-libs/libmpcdec-1.2.6 as well as media-sound/musepack-tools-458 install files /usr/lib64/libmpcdec.{a,so} Reproducible: Always
A bug and not a bug, in a way. An earlier version of media-sound/musepack-tools had a block on media-libs/libmpcdec, this one doesn't probably cause devs thought that it already got purged.
(In reply to comment #1) > A bug and not a bug, in a way. > > An earlier version of media-sound/musepack-tools > had a block on media-libs/libmpcdec, this one doesn't > probably cause devs thought that it already got purged. > The blocker was there for half an year, and then the upgrade path disappeared. emerge -C libmpcdec and profit