I'm having a similar problem.
I've got a splitter with a single pane. I want to create a flyout menu which uses a RadPanelBar for the dynamic menu items and categories. The problem I am facing is that if I don't pre-define the width of the single RadPane in the splitter at design time, the RadPanelBar does not cause the RadSplitter to slide out and present the menu - it's as if it slides UNDER the other content.
I've submitted a trouble ticket and attached screenshots. This is a MOSS solution designed to replace the left hand "quick navigation"
- shows how I'd like the UI to look (ignore styling) with a narrow button for the menu hover-over
- shows how I'd like the UI to look after the menu pops out. Unfortunately I have to preset the width of the RadPane to get this effect. By presetting the width of the RadPane, I lose the screen real-estate I'd prefer to use for content (and have the menu expand over the content)