No. I use a stand alone laptop. Never connected to a larger screen.
occasionally a lcd TV to present photo's in iPhoto.

And the problem is back! No hookups with external displays. Happened
when working on a new diagram.

One possibility here is that there's something that's saved into your default new document template, rather than the preferences. Really, I think the best way to get to the bottom of this would be to [EMAIL="omnigraffle@omnigroup.com"]email the support ninjas[/EMAIL]; we browse the forums as we're able, but support mail will always get a guaranteed response.