I’ve posted this on blenderartists, but I thought it’d be smart to post here as well (someplace not so intrusive). Reposting from blenderartists:
I’m looking for a second set of eyes before I make a report. This bug doesn’t make any sense. I’m scared I’m missing something.
This was something weird I ran into while helping peeps. Changing the collision type of a rigid body (to sphere) makes the behavior all wrong-- even though there’s nothing the RB is collidiing with, nothing it even could collide with, and nothing else changes.
https://pasteall.org/blend/faf19bdeff374ca1a1ec91e233532d02
That’s a 2.83 LTS file, although it’s maybe worth mentioning that the objects were probably originally created in 2.90; I’ve saved in 2.83 as part of testing. (Have also tested with 2.90.1, today’s alpha, today’s beta. Testing RB bugs is a pain…)
So that file as provided works. Notice collision type of “cube” (the only un-animated rigid body) is set to capsule. Play it through, everything works like it ought to.
Now change the collision type to “sphere” and play it through again. All of a sudden, the physics are all screwed up. It seems to be interpreting the constraint completely differently. (And changing collision shape really, really shouldn’t do that…)
I’ve tested in various builds as mentioned, but have only recreated from scratch in 2.83 LTS because it’s such a pain. And there are currently at least 4 builds they’re going to expect to reproduce it. Just looking for somebody else to say, “Yes, report it” or “Don’t, because…”
End repost.
Any feedback on what I ought to do for a bug report on this is appreciated as well. Trying not to waste dev time (and trying to avoid bug report headaches.)