This behavior is related to the floating logic in the current implementation of RadDock. When you float an IDockable window, it is detached from its docking container, and is recreated as a new on host Form object. After this operation, the previous state is not persisted. If you change the DockState the IDockable window is docked as if it was a new one. The state of the IDockable window can currently be restored only for Hide/Show operations.
We are planing to redesign this behavior in our next major version to the RadDock component, planed for Q3 2008.
Thank you for the reported issue. Your Telerik points have been updated.
the Telerik team