Comment 30 for bug 270997

Yannick, you should downgrade your package to the one I'm attaching, just uninstall the current version and install this one.

After that, you should pin the package to this version until this gets fixed (if ever...)
To do that, create a file /etc/apt/preferences with the following contents:

Package: rdesktop
Pin: version 1.6.0-0ubuntu2
Pin-Priority: 1001

And finally symlink this file to /var/lib/synaptic/preferences as apt and synaptic use separate files for pinning but with the same syntax

sudo ln -s /var/lib/synaptic/preferences /etc/apt/preferences