Connecting object blows out the alignment.
 

Longtime Visio user, first-time Omnigraffler here.

I'm seeing this bizarro behavior in which my attempts at connecting two objects with the line tool suddenly splays out every object on the canvas.

Does this ring a bell for anyone? It seems to be specific to this particular document as I can't recreate it on other Omnigraffle docs...

Sounds to me like you've got automatic layout turned on -- You can disable it in the Diagram Layout Inspector.

Keep in mind that the built-in templates in the "Brainstorming" and "Organizational Charts" category have this turned on by default, those in "Drawing" and "Space Planning" do not.

Hope that helps,

That was it. Thanks for the speedy reply!