i think the worst i've had is:
1. view stock
2. trade + confirm (already submitted)
3. go back to view stock
4. open advanced trader in new tab
5. trade + confirm (already submitted)
6. close tab. got to 4 another 4 times
7. trade finally goes through
normally it goes through first time. when it stuffs up average is 2 repeats. it's generally annoying / frustrating as there's nothing to indicate why it would "say" it's already submitted when it hasn't. then just persisting with the trade again suddenly it eventually works. particularly when doing 30+ trades.