How long do you wait before realizing that the system did not get your request? If you want to own some FB stock, and your request is not acknowledged, the obvious thing to do is send another request.
I can see the temptation to just forge ahead on a one time only event like an IPO, but if you do so then I think you need to be prepared for the consequences. I also imagine that part of the usage terms for direct access include something that limit Nasdaq's liability in the event of a system error, so I'm not sure how UBS thinks they will get around that.