XMBC without display connected does not start (Intel H67, Ivy bridge)

Hi,

I have a pretty strange issue with my xmbcbuntu (12.1 installed):

When I start the media center without the hdmi connected to anything, xmbc does not start (cannot find it in the process list).
When it is connected to the TV / projector, even if the TV or projector is off, xmbc does start.

Anyone knows the problem?

It is actually not common, that xbmc is connected to a TV, because I normally use it for playing music only.

Best regards
and thanks a lot for your help!!
Andreas