On June 26, 2013, the stock of Pennsylvania Real Estate Investment Trust (symbol PEI, market cap $1.6 Billion) almost went the way of Anadarko Petroleum (symbol APC, market cap $45 Billion), which traded from $90 down to a penny on May 17, 2013. The reason that APC's stock cratered was because the SEC mandated a new, complicated and untested circuit breaker system called Limit Up/Limit Down (LULD, or LOLZ) and asked the NYSE to stop using their tried and true LRP (Liquidity Replenishment Point) circuit breaker. LRP is the circuit breaker that prevented NYSE listed stocks from trading at ridiculous prices on the day of the flash crash.
After the APC disaster, the NYSE was allowed to reinstate LRP, and for PEI shareholders, that was a good thing. Because on June 26, 2013, NYSE's LRP worked as intended and stopped the price from sliding all the way to zero. The price of the stock did drop lower on other exchanges: probably because those other exchanges don't have NYSE's Super LRP!