The outrage is a bit funny, because that's actually the law in Germany. It doesn't even need to be in the contract. (1) And if you think about it, it makes sense: Otherwise every employee who finds something patentable during working hours just clocks out, goes home and invents it "on his own time." And that would be a problem for an employer, too. So the deal is "employer pays you, and gets first dibs on whatever you invent in the general area that the employer pays you to work in."

(1) https://www.gesetze-im-internet.de/arbnerfg/index.html