I have the same thing as you do in my screen.
I think it's one of the extensions that causes this because first I didn't have it in 2013 and later it does.
I have been able to dock the thing.
I've had the same problem. I think, in my case, it was caused for a 3D Connexion mouse. I recently update it to beta 12 driver. Before that, I think I had ever seen the mysterious floating window. Other things I've done to solve it has been to unistall almost all Revit plugins I had and manually clean any trace of them on C:\Program Files\Autodesk\Revit 2013\Program\AddIns, C:\Users\<username>\AppData\R
Anyway, as I said, I think the problem was the 3D Connexion mouse.
Hope this helps.
Sorry for my poor English.
As someone said, I think the problem is related, in my case, with an ATI card (a FirePro V7800). Changing the 3D configuration makes the windows appear or disappear.
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