I hope I can explain this problem well enough. I am making a saddle for my centaur avatars, which is essentially an invisible vehicle the driver (centaur) and passenger (rider) sit on together. I have two animations I use, one for the centaur walking and one for the centaur standing. Both are priority 4, the main difference is that the walking animation has an arm swing animation, but the standing leaves the top "unanimated" so the avatar will react with the default animations (eg, turn to face chat, type, etc).
The vehicle scripts have a default sit, so I run a llStopAnimation ("sit"

Here's the weird problem: Random top half animations appear--basically one frame of various animation such as typing, the last walking arm swing, even poses my avatar hadn't even used in a day! Thinking that perhaps this was because there was no defining top half anim, I put an AO on that overrides at priority 3, but there was no change.
So, how do I fix this? Any ideas?