Last week, suspected erroneous sell orders in Tata Motors and UltraTech Cement stocks had pulled these counters down by as much as 10 per cent on both the exchanges. Religare Capital Markets had said software technical glitch caused some “unintended transactions” leading to erroneous sell orders in Tata Motors and UltraTech Cement shares. Dalal Street has witnessed a series of freak trades in the last year or so. One of these last year had sent the benchmark indices tumbling. In early October, an erroneous trade punched by a dealer at Mumbai-based broking firm Emkay Global led to the Nifty diving 900 points or more than 15 per cent in a couple of minutes, forcing it to shut down trading for 15 minutes. In December, Sebi unveiled a set of risk controls to avoid flash crashes. The rules involved asking exchanges not to execute a single order in excess of Rs 10 crore.