Just done a test and it definitley seems to be a mod causing the poses to mix in with the dancing animation, not sure which one is causing it as I removed the recent CC poses that started it off so it must be another mod somewhere that needs updating I assume, i'll keep my eyes open and check the mod authors for any updates.
I loaded up a save with all mods disabled and my sim was dancing as normal with no cc poses mixed in, it's not a major issue as the game is still playable, just the dancing looks very odd at the moment :D
