NYSE Euronext said the New York Stock Exchange experienced a systems issue that might have allowed some improper trades. For a brief time, some trades processed at the NYSE despite equal or better prices at competitors. The glitch is the latest in a series of issues at exchanges in recent months. "In scope, this is minor," said Christopher Nagy, a consultant for exchanges and trading firms. "But, combined with this string of events that we've seen, it certainly draws suspicion in terms of what exactly is going on with the stability of the systems at exchanges."