Today I placed a limit order to sell short CUB (AMEX) at 46.19 with TD Ameritrade. At least 15 minutes after I placed the trade, it spiked up to 46.38 but I didn't get filled. I talked to someone in TD Ameritrade trade resolution and he said it was an "intermarket sweep". Is this legit? Does it have anything to do with being an AMEX stock? I've never had anything like that happen to me before. Any insight would be appreciated.