First of all I've been watching the talk segment between 10kies and 11ki members on Girls Live and I don't think Maachan acted bad there (or maybe a bit but I'll explain) before Sakura started to talk she lift up her hand like saying "Dozo (here you go)" but instead of taking down the hand she kept it up, that's the only bad thing I saw her do and that was actually really mild, no one would ever think of that before this incident because it's seriously just Maachan being Maachan and it's why I guess she got most fans because of it.
Where she was pointing at herself and looking at Haruna she didn't either try to interrupt Sakura her she was actually polite (in her own way), she heard something she wanted to add to discussion and wanted to say something. It's like putting up your arm in class, and Ayumi actually said to Masaki that she could go next after Oda so Maachan stood still again and waited for Sakura to finish talking instead of interrupting her.
And now to the big elephant in the room, she cried because Kanon scolded her for getting in the way. First I want to mention (I'm a guy so I can't say I'm an expert at this but still) Maachan is now 15, either she have been in her puberty for a while or just gotten there but the first few years are really tough for both girls and boys when they hit puberty (even more so for girls) they can have heavy mood swings, sure the other handles it much better but Masaki is such a person that she can get really moody she's always been like that (Wotas are always talking about how she either can be really cheerful during handshake, either by jumping up and down, playing games or just love to talk. Then there's days she's quite gloomy and they're trying to cheer her up to no avail).
Damn this is getting really long but still please stay with me (or jump to next post/thread).
Maachan seems to be a person who has to be loved by everyone, and most of those who are outward cheerful mostly are insecure inside. She's mentioned alot of times how she wants to make new friends (the latest Pocket Morning she touched on that subject, that she would use a spell to make people like her more), there was also that time she wanted to buy 40 DS's (most "casual" people still say DS to 3DS so I guess she's talking about that but anyhow), the same segment she said her friends in school teased her for being ugly in the morning (probably it's a joke from them but jokes can hurt too especially if they're said repeatedly).
So why did she cry? We know (atleast assume) that Suzuki scolded her for being in the way during an act, but as lots of people pointed out her jacket was also not shut and broken so probably that was the last thing to completely made her fall down in tears. Then after the performance she was told of by her "kouhai" that her moves and singing were sloppy and that really ruined her day. She had not just let Kanon down, she had also ruined all other nine members performance.
If what I guessed, that she want to be loved by everyone is true, then it's no wonder she lost it and cried alot during backstage afterward. And when you have broken down it's hard to stop crying til' everything is out.
So to sum it all up, Masaki sure was unprofessional but she's just a human, no humans can control every instinct they have and if they could then they would actually be more synthetic than being alive and no one would ever want that.
Also I wanted to point out that Suzuki did the right thing in telling her what she did was wrong, as her sempai she is supposed to tell them what's wrong and not.
About why Masaki went after Reina when she was in the group and then later Michishige is probably not because that she wants to gain more popularity it's just that some people likes to hang out with older people, and she's a long way away from home so it's no strange that she needs a "big sister" in her life. No I don't think that's acting especially because I don't think that Dokkiri prank was staged, the way Sato hugged Sayumi when falling asleep shows how much she needs her.
Sorry for all this text, but sometime when I start writing I can't stop until I'm completely done