My theory as to the problem/issue (which I think I discussed awhile back) is the programmers did not address the issue of multiple e-ticket issuance on a single PNR. Ticket stock (e or paper) is limited to four segments per single ticket number. A paper ticket of 6 segments will actually have 1 ticket # for the first 4, and the sequential # for the last 2. UA can issue tickets like this, and so can travel-agency booked tickets, all on e-ticket "stock". So there you have the problem, IM(nsh)O.