Board Thread:Speculation House/@comment-14138255-20140815002519/@comment-24106129-20140822011347

VedranTheII wrote: So then why did she decide out of the blue to tell Blake without Yangs consent? She could have gone “She’ll be fine, look!!!”. Shorter to say, would have given Blake pause long enough to notice Yangs fine and most importantly, would have not revealed Yangs supposedly hated semblance to everyone within earshot. Yeah, I'm not buying it... She decided to tell her out of the blue because that exposition was forced, poor in other words. The basis behind it was that Yang had never fought using her Sembalance in a team with RWBY, although Blake might've been watching her fighting the Ursa in the pairing ceremony.

Zolnir Qrow and other faculty members are probably aware of her Sembalance and the reason you are suprised that nobody found out is because it's convienent for Ruby's jumble of words for Yang's exposition.