1. boot to desktop with no external monitor connected
2. Open the "Display" utility, check whether there is an "Unknown" display. You will be able to move the cursor out of your screen, even open an application on the extended display.
Tested with 2015-01-29 drm-intel-nightly.
00:02.0 VGA compatible controller : Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller [8086:0106] (rev 09) (prog-if 00 [VGA controller])
01:00.0 VGA compatible controller : NVIDIA Corporation GF108M [GeForce GT 630M] [10de:0de9] (rev a1) (prog-if 00 [VGA controller])
Original bug: https://bugs.launchpad.net/ubuntu/+source/linux-lts-trusty/+bug/1355562
I'm guessing this is a muxed hybrid laptop? We hit a similar issue in radeon. Basically the desktop environment doesn't understand muxed displays so it reports the status of both GPUs. Arguably vgaswitcheroo needs to be augmented to properly report the mux information so userspace can do the right thing with respect to muxed laptops, but a short term fix would be to just report disconnected on whatever GPU is not currently selected via the mux.