selection an output's resolution with tab renders whole x session unusable

[Bronsen]

I had started arandr and activated one output using only the keyboard; the output was activated using <enter>. Then I wanted to tweak that output's resolution --again, using the keyboard-- , so I navigated to the desired resolution and attempted to activate it using <space> and not <enter>.

This essentially seemed to stop my whole x screen: only the mouse cursor was moving around, but no other actions where possible. After killing the arandr process from the text console (C-A-F1 still worked, yay) my x session was working again.

arandr spat out the following message:

/usr/lib/python2.7/dist-packages/screenlayout/gui.py:300: GtkWarning: IA__gtk_widget_event: assertion 'WIDGET_REALIZED_FOR_EVENT (widget, event)' failed
  gtk.main()

This happens with arandr on vivid:
$ apt-cache policy arandr
arandr:
  Installed: 0.1.7.1-1
  Candidate: 0.1.7.1-1
  Version table:
 *** 0.1.7.1-1 0
        500 http://de.archive.ubuntu.com/ubuntu/ vivid/universe amd64 Packages
        100 /var/lib/dpkg/status
$ lsb_release -rd
Description: Ubuntu 15.04
Release: 15.04

[Bronsen (housetier-deactivatedaccount)]

Tweaking that output's resolution via keyboard, but using <enter> does not yield this behavior.