Reasonable bid-ask spread is not enforced for ETFs

Trading was halted 1,200 times Monday August 24, 2015
http://www.kwch.com/trading-was-halted-1200-times-monday/34891690

Alarming ETF meltdown

ETF.com examined the pricing action and discovered at least eight ETFs that showed "flash-crash" style drops at the opening of trading.A number of them are tiny ETFs like the iShares Core Conservative Allocation ETF and Emerging Markets Internet & Ecommerce ETF. In some ways, that may be expected given how smaller ETFs lack liquidity -- the ability to quickly get in and out of a security, even during market turbulence.
Large ETFs mysteriously dive
Yet other ETFs that experienced panic selling are far larger and wouldn't be expected to have that kind of turbulence. For example, the iShares Select Dividend ETF plummeted as much as 35% at its lows.
That's a stunning move considering this BlackRock-backed ETF is worth over $13 billion and is focused on stable American stocks that have a long history of paying dividends.
None of this ETF's top holdings -- like Lockheed Martin, Philip Morris International and McDonald's -- suffered losses north of 11%.
It was even worse for the Guggenheim S&P 500 equal weight ETF. The $10 billion fund, which holds some well-known stocks like Chipotle and ConAgra, plummeted nearly 43% at one point on Monday.Another popular ETF that seeks to capitalize on the booming cybersecurity business plummeted as much as 32%. The ETF, PureFunds ISE Cyber Security ETF, has a market value of more than $1.2 billion.

Mini Flash Crash Bites Some ETFs
http://www.etf.com/sections/features-and-news/mini-flash-crash-bites-some-etfs

ETFs flirt with 50-plus-percent losses—all while the S&P 500 registered a 4 percent decline.
These weren’t illiquid, small ETFs either. The iShares Select Dividend (DVY | A-69) traded some 36 percent lower; the Guggenheim S&P 500 Equal Weight (RSP | A-83) hit a 42 percent drop and the iShares Conservative Allocation Fund (AOK) traded roughly 50 percent below its Friday close.
In addition, the iShares S&P Mid-Cap 400 Growth (IJK | A-77), the iShares U.S. Broker-Dealers (IAI | C-76), the PureFunds ISE Cyber Security ETF (HACK | C-26) and the Emerging Markets Internet & Ecommerce Fund (EMQQ | F-20) were also among the ETFs hit the hardest, according to sources.
ETF.COM ANALYST BLOGS
Understanding ETF ‘Flash Crashes’
By Dave Nadig
http://www.etf.com/sections/blog/understanding-etf-flash-crashes

May 6 2010 ETF Flush Crash -
Understanding the “Flash Crash” - BlackRock
https://www.blackrock.com/corporate/en-ch/literature/whitepaper/understanding-the-flash-crash-nov-2010.pdf