Odd textures in the sky

Quite often I see some odd very light white textures in the sky. When I move my head around the textures stay where they are and so they seem to be in the far away distance, as if they are very light clouds. However, the odd thing is the textures move along with the airplane! I only see them when I am in the cockpit (of the Airbus which I mainly fly, I haven't tested this yet with other planes). When I switch to an outside view I don't see this. So it sort of seems some sort of window thing... but that doesn't make sense because as I said, when I move my head the textures stay stuck in the sky... if you know what I mean.

Hope you can see what I mean on this screenshot. As you can see it looks a bit like some dirt or fog on the window but when you move your head it looks like far away clouds: they don't stick to the window then. (Hard to explain LOL)

O, and this texture often suddenly disappears or changes...

No, not reflections. First of all when I bank left or right the reflections appear to be in the sky, as far away as the clouds, not on the window. They aren't stuck on the window. They retain their position to the landscape. At the same time they move along with the plane. And also they suddenly disappear or change.