This part in src_install replaces the log files if already present. | insinto /var/log | touch ${T}/blah | insopts -m0640 -o mpd -g audio | newins ${T}/blah mpd.log | newins ${T}/blah mpd.error.log How about checking it in the init file?
Wow, this bug is almost exactly one year old. I wonder how I missed it. Anyway, this has been fixed in 0.12* ebuilds for a long time now, now we just create /var/log/mpd directory and let mpd create log files. Bug #154742 has just been opened to make a 0.12* ebuild stable, so this should no longer be an issue.
As 0.12.1 has the same keywords as 0.11.5-r2, I'm closing this bug.