MariaDB will not bind to "localhost" if localhost is both IPv4/IPv6 enabled
If a host is configured with both an IPv6 and an IPv4 address, MariaDB will not start up. This was reported against mysql in http://bugs.mysql.com/bug.php?id=61713, and was later fixed. This fix is not in MariaDB.
I would also note that the mysql folks fixed it incorrectly. Please see http://bugs.mysql.com/bug.php?id=65122 for the follow up.
We are looking at migrating from MySQL to using MariaDB, but this inability to properly support IPv6 means that migration is a no-starter. I am astonished that since this was already at least partially fixed in MySQL it is not already in MariaDB.