For start, bin/mailmanctl is missing so as a lot of other files from bin Reproducible: Always
It is installing all nesesery files, but in different location. The error appears if mailman is upgraded from an older version, and mailman account is already present on the system, because home dir changed, and init script runs mailmanctl as "bin/mailmanctl".What would be the best way to correct this? If user exists, modify the home dir? Anyway, I can not restore old lists, even with all above corrected.
For old list, you'll have to copy data over (from /usr/local/mailman/* to /var/lib/mailman). Or change the variables (documented in the ewarn section of the ebuild) to the old location. The homedir must be changed manually, but now the ebuild warns about that.