>the last thing you'd want to do is to work after-hours and find out your employer is owning the IP of your project

Has this ever happened? I would imagine that if some guy got his FU money taken away and given to some big company where it would be too small to even register on the income statements that said person wouldn't just lay there and take it.

After all, what you're describing is literally slavery (i.e. anything the slave makes belongs to his/her owner).