(this is on 2.2 i dont know if this happens on other relases)
i was trying the joints stuff on scene designer to learn about it because i didnt found a real tutorial
but then i found some of bugs that make it practically useless for example
i made a hinge joint and now sometimes i cant delete it and when i make for example a sliding joint after the hinge joint i CANT EDIT sliding joint data because it appears the data of the hinge joint

(on that inspector thing) and never goes
i dont want to annoy jon and company(maybe they have a lot of work right now) but i think i needed to share this so this gets fixed one day