The problem seems to be related to the way Silverlight framework works. If the HTML element, in which the Silverlight content resides, is moved in the DOM tree the Silverlight content gets refreshed.
This is actually how the Drag and Drop functionality of the RadDock control works. When the RadDock control is moved it is actually moved in the DOM tree. Basically, if the dock is docked to a zone, its wrapping HTML element is a child to the RadDockZone's element, and if floating it's a child to the <form/> element. So, if the user moves the dock from a zone to a zone, or undocks/docks it from/to a zone, the dock's element changes its parent.
To demonstrate that this issue is browser related behavior, I have created a sample project that moves the Silverlight content in the DOM tree. Please find it attached to the thread. I have searched for a solution to work around this issue, but couldn't find any.
the Telerik team