To reproduce:
Dock a window under another with these themes( blue black silver): instead of docking under, it docks overs as if over the tab icon instead of the down arrow.

Workaround:

-Extract the predefined themes 
-Open the Office2010blue theme with Visual Style Builder
-In the control structure window select RadDock - Docking Guides
-Expand DockingGuidesElement and select BottomImage
-In the Elements window expand DockingGuidesElement and set filter to changed properties
-Change LocationOnCenterGuide property to 45;90
-Save the theme and use it in your application