When RadWindow is being dragged/moved it is expected the content area to hide itself. This is a prevention of a browser behavior. Typically, when dragging DOM elements (like RadWindow) browser enables end user to drop this DOM element in content editable areas (like the content area of RadEditor).
Therefore, to overcome this unwanted behavior and prevent outside DOM elements to get into the HTML of the content area, when RadWindow is being moved around, the iframe element hides itself.
I have tested with RadWindowManager, but still I was unable to encounter the described situation. Apart the one related to moving the RadWindow.
I suggest you to try and isolate the case in the sent example and attach it to your message in order to examine the exact scenario that is on your end.
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