Seems to be random,

I recorded both events of this "dancing" with MSI Afterburner.

First event: http://www.youtube.com/watch?v=VESlvpf7l_E&feature=youtu.be

Second event: http://www.youtube.com/watch?v=p45VdNLH8ng&feature=youtu.be

Sorry about the quality, but I don't know how to upload it in its original resolution to youtube. You should be able to see what is going on though.

Before I submit this, I will try the night showcase again to see if it happens again. Results: I just started the night showcase and ran straight up to the lighthouse, and they were not dancing this time.

Also, just to be clear, I am not pressing any buttons except alt for looking around, and the movement keys(wasd), as well as using the mouse.

I have some more info: My friend and I were playing the combined arms mission and the apc blew up next to us. He started laughing and told me his guy was freaking out. I asked him what was happening and he just told me his guy was bugging out and moving his arms weird. So I asked him if my guy was doing it, and he said yes. I didnt see my guy doing anything strange, or his character. I asked him if my guy was still doing it and i walked away from the wrecked apc. He said they stopped bugging out("dancing") as we moved away. So I gathered some more info:

1. the bug is clientside, so in multiplayer, 2 players might not see the glitch happening.

2. It has something to do with either car wrecks, or the fire(I think the fire).