Ahh. When will people realise that idols are people too? :/ They get tired from performing just like you or I would. Why blame them for being so tired they can't even fake a big smile on stage. I mean, seriously, how tired would she have been to not be able to pretend to be happy or, as they say, 'look like she wants to be there'. Jeez. People need to not take these things so seriously.
I just hope T-ara get the rest they need and stay healthy. I don't care about their face expressions during performances if all they do is appear expressionless every once in a while. These girls need rest.