Now the graphics are saved but the magnitude/brightness not!
I'm pretty sure that magnitude settings have never been saveable, and always revert to default at startup. This is probably a good idea since setting a very high magnitude for stars while in the galactic core will lead to an attempt to generate many billions of objects, and your computer will crash. Resetting to default on startup protects you from not being able to run the program if you try to open it again in the same location.
Very old versions of SE had ability to save magnitude settings. In addition to constantly crashing in the galaxy center, due to a very high magnitude limit. I ofter receive "bug reports" of no stars or galaxies being visible. Guys, just set it too low magnitude and forget about it.