OK, I'm now testing 20130423.2 amd64 and I still get a freeze at this point although bug #1080701 appears to me to be fixed.
To be clear; it's not possible to "drag" to resize and only the quit button appears to be active (although it doesn't work), even clicking on the highlighted "advanced partitioning tool" does nothing so install alongside is borked in Ubuntu GNOME.
It does work OK in Lubuntu so I think this is purely an Ubuntu GNOME problem, but I've not had time to test Ubuntu itself.
OK, I'm now testing 20130423.2 amd64 and I still get a freeze at this point although bug #1080701 appears to me to be fixed.
To be clear; it's not possible to "drag" to resize and only the quit button appears to be active (although it doesn't work), even clicking on the highlighted "advanced partitioning tool" does nothing so install alongside is borked in Ubuntu GNOME.
It does work OK in Lubuntu so I think this is purely an Ubuntu GNOME problem, but I've not had time to test Ubuntu itself.