TrishAce Resident
It is possible for a vehicle to be in a state where it "settles" in a way that sends no more viewer updates. When that happens, the viewer will try to interpolate the last tiny omega value forever.
To reproduce this, you need a vehicle that does not resend llSetMotorParams on a forever loop. (Some vehicles will spam a speed of 0 while stopped, which will make them slide in slopes and effectively prevents this bug from happening). The 777 2PM freebie from a previous shop n hop is one of the vehicles that can reproduce this bug. (I also have an old version of a vehicle Ive worked on that can suffer from this, if you want, I can provide a trimmed version for testing purposes)
Then the repro steps is:
  • Stop in a slope at an angle
That's it!
You will notice a stutter happen (this is the movement interpolation fighting the real state of the object), it corrects itself when the object refreshes, but sometimes it will forever interpolate until you right click or refresh in some other way:
https://gyazo.com/3c3670b25577d23a168e74b4de890a09
Side note, to prove this is interpolation-related: altering the InterpolationPhaseOut setting affects that stutter, a value of 0s will guarantee you have a spinning moment, the default of 1s makes it stutter, having it at something like 0.001s completely kills the stutter and feels as it should, you dont get a bunch of micro stutters: https://gyazo.com/de896f5d97fa8eb2e249aa30385a0953
Multiple people on multiple viewer may see a different spinning state based on when they last got an object update. Ive had cases where I see it spinning and a friend doesn't, and vice-versa. This bug happens both on the LL viewer and Firestorm and Alchemy.
Another case here:
https://gyazo.com/a23fde28fb036c85bb5c066946261cd2
now 3 minutes later:
https://gyazo.com/0bf78e44ad27ec2892de41ced7babb3e
right clicking, or otherwise interacting with the vehicle in some ways makes it reset upright as you would expect:
https://gyazo.com/2288c60146f75541bedf4c2a6f3e6801
From my troubleshooting with my own vehicles scripts & some viewer tinkering, the engine/scripts sees the car in its "true" orientation.
I've managed to "fix" this quirk by forcing object updates in my lsl script. (Like by changing some invisible hovertext), but the real fix would be to adjust viewer interpolation for vehicles to prevent them from spinning endlessly.