Comment 3 for bug 703240

Test case (always reproducible)
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1) Install a prior version of a package; for example:

apt-get -f install python-apport=1.14.1-0ubuntu8

2) Go to «Software Center» --- "Gestor de Software" in spanish

3) Select update. There should notify that the package downgraded previously is available for upgrade

4) Select upgrade. Then the sudo password dialogue window should appear. Put sudo password

--- the dialog-window gets stuck, both buttons (cancel and authenticate) don't work --- see screenshot attached

Workaround: close the window pressing the "X" on the left-top.

As the window is closed, the install proceeds normally