"At the open, most markets except for the NYSE opened at 9:30, and if you're trading an S&P ETF and 50 percent of the S&P is not open, you have some pricing challenges on your hands," said Chris Concannon, head of exchange operator BATS Global Markets.

In the fallout of the pricing problems, ETF provider The Vanguard Group said it was going over all of the trades on Monday to see if investors should have gotten different prices than they did. However there is no recourse for these investors because the rule for erroneous trades require investors to notify the exchanges within 30 minutes if they got a bad price.

The "clearly erroneous" trades rule is a standard definition of trades that exchanges will cancel if executed, based on how far away from the public stock price they are, and it too was updated after the flash crash.

Some, like Cantor's Browne, thing those rules also need tweaking, but the SEC believes that rule could become redundant if the exchanges get the Limit Up Limit Down rules right.

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