Hi Falk Wegener,
Thank you for writing.
Your DockPanel is attached to a TabbedDocument container and its state cannot be a AutoHide. Please first change the DockPanels to a Docked state like ToolWindow and then you can change the state to AutoHide.
The behavior is like Visual Studio Docking.
I hope this helps. If you have additional questions, please contact us.
the Telerik team