Sit animation from AO won't override default sit?

[cicadaserenade]

I have tried both the AO from the AO's creator and placing an animation into FS's AO. Both result in a borked sit animation where the top is animating correctly, and the bottom half is that of the default sit animation. I have tried multiple sit animations from multiple, popular creators (LeRoux, Russkaya, Body Language, etc.); all of them result in this kind of mash-up.

Here is what the animation list looks like when I sit on a cube:

 

Here is what it looks like when I just play the animation locally:

 

This leads me to believe it's not a priority issue. Then again, I don't know anything about animations. lol So please explain it to me like I'm five: how do I fix this?? I'd really appreciate the help!