I have tried to place a small BTC limit order at 5823 on Bitstamp Trading screen, but it was immediately executed at current price (5777)

Now the unwanted transaction is recorded in my HISTORY screen, my balance shows the corresponding BTC amount prematurely bought and just a couple of cents in EUR.
Fair enough, I might have made an error, even if it did not look so. But now, in the TRANSACTION screen, I can ALSO see my limit order correctly opened and waiting to be executed. The OPEN ORDERS screen does not show the limit order, so I do not have an option to Cancel the limit order.
Now I wonder: what will happen if the limit order is triggered at 5823 while my EUR account is practically empty?
Should I open a ticket there?