apt-get wants to remove MariaDB on Debian Wheezy

I've set up my server to use MariaDB and used the installation instructions on the web page. It worked quite well. Now, if I want to dist-upgrade, apt-get wants to replace MariaDB with MySQL:

The following packages will be REMOVED:
  libmariadbclient18 mariadb-client-5.5 mariadb-client-core-5.5 mariadb-server mariadb-server-5.5 mariadb-server-core-5.5
...
The following packages will be upgraded:
  libmysqlclient18 mysql-common

Why does apt-get want to do this? How can I stop apt-get from doing so?

Unfortunately, this is a known problem, with an already-filed bug report: see here. The conflict arises because mysql and mariadb use conflicting versions of the library libmysqlclient18.

The quick fix is to give mariadb a higher priority than mysql, I have done it like this:

 echo -e "Package: libmysqlclient18\nPin: origin mirror2.hs-esslingen.de\nPin-Priority: 1000" > /etc/apt/preferences.d/mariadb-mysqlclient18

(This is for my mirror, of course... You'll have to adjust the above command to your mirror).

I agree it should be fixed upstream, but in the meantime...