When you "mousedown" on the dock's titlebar (which is fired before "mouseclick") you are actually starting to drag the RadDock, and all of the client-side events related to the dock's movement (OnClientDragStart, OnClientDrag, etc.
) are fired. This behavior cannot be changed, but if you want to disable dragging (movement) of the RadDocks you can use the EnableDrag="false".
Let us know if you have other questions.
the Telerik team