ShowMySky GUI: horizon not centered when running maximized window

[Atque]

Using my 2560x1440 monitor, ShowMySky GUI lifts the horizon above the center of the screen when running window maximized, see the screenshot below:

Reloading shaders does not help, nor does any of the other options.

[10110111]

Funny. And what if you just resize the window instead of maximizing it?

[Atque]

Funny. And what if you just resize the window instead of maximizing it?

Same result. Dragging the corners of the screen the slightest, causes the horizon to lift.

Interestingly, maximizing the window before the textures fully load allows me to run maximized with no problem. However, resizing the window afterwards reproduces the problem.