IIRC Dr Stipp doesn't explicitly say but Annette Stipp says the left side of the bathroom window was slid open. I take your point about seeing a figure moving though the frosted glass. I'll have to check but it would contradict his wife if he means all three panes.
I'm not sure .. just going by Lisa's blog ..
Mrs Stipp:
"Nel asks her if she also saw the man walking in the house, just as her husband did, but she did not. She is aware that in her statement she originally said she did but after really thinking about it, she did not, so she had them change it.
Mrs. Stipp also stated the house that they saw to the right of Oscar’s from their bedroom balcony had all of their lights on in the top story of the home. The house on the left (Oscar’s) has two sets of windows (one is the toilet room window and the other is the larger bathroom window) and one of the windows was open.
Here is an aerial view of Oscar’s bathroom windows. The toilet room window is on the left (the smaller one). The bathroom window is on the right. The white circle indicates the portion of the window that was open. According to Mrs. Stipp, the light remained on the entire time".
and Mr Stipp:
"Now, they are back to discussing Dr. Stipp’s vantage point. They review photos so Roux can understand what he saw. Dr. Stipp explains that he could see the top half of the middle and right window and all of the left window. Parts of the windows to the right are obstructed by trees, that is why he only saw half of those. The bathroom windows consist of 3 sections and according to Oscar, it was the section on the left that was open (if you are looking at the windows from the outside). Here is a photo of the windows from the inside – so it would be the window section closest to the toilet door on the right that Oscar states was open. Roux wants to know how Dr. Stipp saw a figure moving in the window since the windows are frosted. He assumes it’s because the window on the left is open and he can see the figure through that open space. Surprisingly, Dr. Stipp states that he doesn’t recall that window being open. This would be another huge problem for Oscar. The window being open is one of the things that supposedly freaked him out so much that he went in to full blown terror mode thinking there was an intruder in there. But Dr. Stipp states that he can’t definitely say if it was open or closed, just that he doesn’t recall that it looked open. Roux states they have pictures from the scene and puts the kibosh to that conversation quickly."
.. reading through the whole blog for both of the Stipps, neither of them appear to say they saw the window open (and Dr Stipp sounded pretty sure it was shut, i.e. he was seeing the figure through frosted glass but seems to have been persauded otherwise .. i.e. that he must've been mistaken and that the window must've been open). Mrs Stipp doesn't appear to have said it was open at all, she just refers to the light being on. Of course, I would really need to read through an actual transcript to be absolutely certain of what was said.