leap-mx not installable due to unsatisfied version dependencies

on a fresh, upgraded wheezy server:

root@rewdevplain1:~# apt-get install leap-mx
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 leap-mx : Depends: python-twisted (>= 13.0.0-1~bpo70+1) but 12.0.0-1 is to be installed
E: Unable to correct problems, you have held broken packages.

(from redmine: created on 2014-03-07, closed on 2014-03-07)