Blink and you may have missed it.
Dollar Tree, the discount retailer that sells everything for $1 or less, suffered a mini "flash crash" in the first two seconds after the open Thursday.
The stock plunged 18 percent before snapping back to more normal levels less than two seconds later.
"At the end of the day, this kind of stuff is going to be ongoing because the machines are contributing the only margin that's really left in the broker-dealer community," he said. "You saw this issue with Knight Capital." (Read More: Knight Capital Type ‘Glitch’ Will Happen Again).
"We think these issues are endemic and structural," McCullough said. "They're not going to do anything for investor confidence."
Dollar Tree had warned earlier that its third-quarter results would miss analyst expectations. The retailer expects earnings of of 47 cents to 51 cents a share on revenues of $1.71 billion to $1.75 billion for the current quarter. Analysts on average forecast earnings of 52 cents a share on sales of $1.77 billion.
For the second quarter, Dollar Tree met analyst expectations with earnings of 51 cents a share, up from 39 cents a share a year earlier.
Sales rose 10.5 percent to $1.70 billion, while same-store sales climbed 4.5 percent, down from a 4.7 percent increase a year earlier.