System environment:
chipset: G45
uname -m: x86_64
libdirm: 2.4.11
kernel: 2.6.30-rc8
distri: Ubuntu Jaunty
Board: GA-EG45M-DS2H
Display: HDMI Panasonic

Description:
While booting my system with monitor powered off, Xorg won't start and crashes with:

(EE) intel(0): No valid modes.

Backtrace:
0: /usr/bin/X(xorg_backtrace+0x26) [0x4f1d86]
1: /usr/bin/X(xf86SigHandler+0x41) [0x478311]
2: /lib/libc.so.6 [0x7f88e2ef6040]
3: /usr/lib/xorg/modules/drivers//intel_drv.so [0x7f88e0f3ccc6]
4: /usr/bin/X(xf86DeleteScreen+0x7e) [0x48086e]
5: /usr/bin/X(InitOutput+0xe1d) [0x46fbdd]
6: /usr/bin/X(main+0x20e) [0x433d2e]
7: /lib/libc.so.6(__libc_start_main+0xe6) [0x7f88e2ee15a6]
8: /usr/bin/X [0x433369]
Saw signal 11.  Server aborting.
 ddxSigGiveUp: Closing log

See full Xorg.0.log.

When monitor is powered on, Xorg starts perfect with the correct modes.
Xorg should start always, also without monitor connected. 

Reproducing steps:
Boot system without monitors connected.