I think this is what is happening to me right now and after 5 hours on the phone dealing with the TOTAL BS of the new UA maybe this may be helpful to some:

If you look for inventory like me and see an F seat but agent says NO "not available" ( I am trying to do a stopover trip and can not book online!) try to book it on line, when you get to the payment page hit the "phone order" link or something like that...if you get an error page than that inventory does not really exist...if it does it should give you a conf. # to call in with...

One step forward and two back with the new website...

Keep up the great work Smi/J