the dev-libs/mm ebuild should inform the user that he might want to run revdep-rebuild after an upgrade of mm. it just broke my php5 here because /usr/lib/apache2/modules/libphp5.so links against libmm.so.12 and the upgraded version (1.3.0) has libmm.so.13.
added - I'm sure the upstream ABI versioning is wrong anyway. Thanks for the bug report.
and closing...