I don't think Paulina Rubio shaded Britney. Paulina has used playback plenty of times though she does sing live as well, no fan can deny that.
It started off as a compliment and she ended up screwing it up and not knowing what else to say from what it seems and this guy from Breathe Heavy got butthurt over her saying that so he probably said it was shade cuz they know the Army would go IN on Paulina. & Let's be honest here Britney is mostly known for using a head piece than a microphone so she isn't lying there if she really said that.
Love both of my Queens