Not sure omeyer because of the huge number of dependencies if the pinning keeps versions over security updates and as things are added there is a chance down the line over time that it might.
Zentyal is slowly moving away from there repo's to becoming an all ubuntu repo, so I thought anyway.
Even though I was great full of your fix I decided just to wait as I don't like making any changes of forcing dependencies.
I have in the past and then found a long way down the line, circular dependencies "dependency hell" where I have been unable to find a route out.
I am just playing safe, its been fixed don't deviate. Just a rule of thumb for me.