Upgrade from galera-server-5.5.46 to galera-server-5.5.47 changes the root password

I have an install of Debian 7 with mariadb-galera 5.5.46 on it and have set a mysql root password, everything works fine.

The folllowing behaviour is the same whether the machine is a standalone mariadb install or it if is clustered.

I upgrade to mariadb-galera 5.5.47 (using dpkg directly and upgrading all the pre-reqs as well) and when the DB server restarts at the end of installing the mariadb-galera-5.5 package it changes all the root password lines in the mysql.user table.

I was running a loop doing "cat /var/lib/mysql/mysql/user.MYD" and I could see the hash for all the root passwords change as soon as mysql started.

This obviously leaves me unable to login to the DB as root.

If I save the user.MYD file away, run the install and then put the old user.MYD back in place then I can use my root password to access the DB and further restarts of mariadb do NOT change the root password.

Is there some flag I can pass to dpkg when it installs mariadb-galera-5.5 so that the root password does not get changed?