To all you doubters out there, there is an article on this subject in April’s Sky at Night magazine – – -!
The article says “Observing through a closed window is not recommended due to reflections and distortions”
A closed window prevents air currents and that is much better than an open window. If you are in a dark room and the telescope objective is close to the window the “reflections and distortions” are minimised.
Take a look at some of my window-sill images if you don’t believe that!