netbook-launcher will not start with external monitor connected

[Paul Natsuo Kishimoto]

My hardware is an Acer Aspire One 110L.

When only the built-in display of the laptop is active, netbook-launcher runs without issue.

When I have an external monitor connected, netbook-launcher will not start.

Attached are the output of two commands:
$ sh -c "CLUTTER_VBLANK=none netbook-launcher" >netbook-launcher-single.txt 2>&1
$ sh -c "CLUTTER_VBLANK=none netbook-launcher" >netbook-launcher-dual.txt 2>&1

...in the first case (built-in display only), I terminate netbook-launcher with Ctrl+C. In the second case (external monitor connected), the command returns and the launcher is not displayed.

[Paul Natsuo Kishimoto (khaeru)]

On further examination, this appears to only happen when I use gnome-display-properties to rotate the display on the external monitor.