Hi Sebastian,
Maybe you should ask before report something as a bug

your not batting too good.

1 and 2 occur because you have the Terrain turned on. Turn it off in the View Manager. The terrain is part of the 'extents'
3 Havent' tested.
4. Repair function doesn't remove my floors, if you have used the Room Division tool it can corrupt the floors and repair would remove them. Of all the tools I have the hardest time with Room Division.
5 Haven't tested
6 Blue color is the 'sky' you are seeing through the terrain. Try switch to an Entry Door that contains a Sill. Hinged doors have no full sill and are better for interior walls.
7.No problem exporting image , no squezing seen, I do not change the default size settings and I zoom to screen the image I want to export.
8 Am / PM is built into the Global time which takes the place of 24 hrs setting. Uncheck "Use Current Time' to access them.
take your time and experiment a bit. the program has features in it that are different than what you may be use to.
I have found very few bugs at all in the program.