^oh, I read what I wrote maybe I didn't make myself clear xD, what I meant to say is that they've been adding some parts of the song "live" from some time now in this particular performance they are singing live just the first part of the song, and yes they've sang full songs live just like
BCL and many others.
And in this latest MS performance they are mixing it again, if you notice for the first part of the song they are not in perfect sync with each other and when they hold the notes they go a bit off key. Towards the chorus we hear more of the synth voices 'till it shadows the girl's voices and that's when the chorus kicks in their voices sound heavily synth.
Another example of this is on Music Japan's live where they sang polyrhythm, just after the cool dance break they sing live and the sythn voice starts again when they say the first "meguri" (after kashiyuka) link:
http://mx.youtube.com/watch?v=RwQsuiWZXXg (when a-chan sings you hear clearly she's singing live).
so, I think is cool they mixing it up, tho they should do more lives like the first BcL. =D.