This is where I first noticed it. And most every other pic I've seen I can now see it. I can also see something of the separations between panels.
It's hard to notice because most images have the bottom edges of the windows almost at eye level. And with only a 2-3 degree difference between panels it would be very easy to miss.
I myself thought it might be an illusion or a distortion in the photograph, but once I saw it it began to be obvious to me. It's even more obvious in the colour pic you posted. But I wanted confirmation so I asked Gary Kerr who has been spending quite a bit of time researching and developing plans for Round2's shuttlecraft model kit, including an interior, and he confirmed what I could see.
Why would someone build it that way? Possibly because it was important enough to them to be as detailed as possible even given time and budgetary constraints whereas most anyone else wouldn't bother.
I think a two- to three-degree difference in the three different planes isn't "easy to miss" so much as it is "easy to hallucinate."