itunes activates unchecked songs after launch (without asking)

Every time I launch iTunes the first time after booting up the PC, it activates around 300 songs I didn't listen for years (so I unchecked them, but they were still in my media library).

It seems to be iTunes looked up all my purchases and activated/checked them again without asking.

When I restore my library, it only takes a few seconds and the songs are there again.

I unchecked every automatically download settings and so on, I also deactivated Genius.

I don't want to delete my songs, I just want them to stay unchecked. I also fear they would come up then as checked and downloadable. I also deinstalled all iTunes components in the right order but it didn't help either.

I don't know what to do, and I didn't find anyone else with this crazy problem.