My theory about the Mtgox fiasco is this:
When he was forced to liquidate bitcoins he might had to sell more bitcoins than he had bought if liquidity was very low. So the extra bitcoins had to be created from thin air which caused a btc fractional reserve. Same logic applies if he wanted to create a downtrend with a fiat fractional reserve as a consequence.
Maybe I am uninformed well or my knowledge about Mt Gox and its story are outdated but my memory tell me that there were a hacking tentative in this company which has stolen thousand of bitcoins.
Both the theories that Mt. Gox had been operating on a so called "fractional reserve" for some time [not genuinely possible since it never loaned bitcoins back out as a fractional reserve bank might do], or that it had suffered a major loss through hacking have been cast into serious doubt by the recent justification used by the Tokyo police in arresting Mark Karpeles:
"Police suspect Mark Karpeles padded his bitcoin outstanding balance by illegally manipulating his company's computer system.
His Tokyo-based company, MtGox, suddenly stopped all trading in February last year and filed for bankruptcy. Karpeles announced that 650-thousand bitcoins, worth more than eight billion yen at that time, had disappeared.
He claimed the exchange collapsed after hackers stole most of his clients' Bitcoins. But police say most of the bitcoins held by the company were sent to another account.
Police believe Karpeles knows what happened to the virtual money." [emphasis added]
See:
http://www3.nhk.or.jp/nhkworld/english/news/20150801_05.html
