Interesting, I can confirm this doesn't happen while my laptop display is turned on (although it doesn't have to be set as Primary).
Here's my GPU info, currently leave nvidia card off using Bumblebee:
lspci -vnn | grep VGA -A 9
00:02.0 VGA compatible controller [0300]: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller [8086:0126] (rev 09) (prog-if 00 [VGA controller])
Subsystem: CLEVO/KAPOK Computer Device [1558:5140]
Flags: bus master, fast devsel, latency 0, IRQ 27
Memory at f1000000 (64-bit, non-prefetchable) [size=4M]
Memory at e0000000 (64-bit, prefetchable) [size=256M]
I/O ports at 5000 [size=64]
[virtual] Expansion ROM at 000c0000 [disabled] [size=128K]
Capabilities: <access denied>
Kernel driver in use: i915
Kernel modules: i915
--
01:00.0 VGA compatible controller [0300]: NVIDIA Corporation GF108M [GeForce GT 540M] [10de:0df4] (rev ff) (prog-if ff)
!!! Unknown header type 7f
Kernel modules: nouveau