Hi tzimasr
I think this is the first time you reported an actual issue
Backgrounds like these typically use a
skybox, and it seems something went wrong here. I've seen this problem in most of the tracks, so i guess this is not a problem with the textures, but some small bug in the engine. Usually, it is not quite noticeable, as the camera rarely uses a pitch angle that makes the top or bottom of the skybox visible. Mhm, maybe this has even already been fixed in the development version.
If you have that many "bug" reports, maybe it is a good idea to collect them in a single topic? And hey, don't tell the devs they "must fix it" each time you report something