I'm still not clear on the processes, but here is what happened:

1) Built reservation on united.com; it did not ticket and just disappeared

2) Called premier line a few days later and got an off-shore agent. After about 40 min. and much hold-while-I-consult, she rebuilt the itinerary in the same record (which still existed, but had no flights). When she got to the EI flight, she said it was "unconfirmed" which meant that it was not available. She proceeded to explain to me how airlines manage award inventory...irritating. After the call, the flights were back, but disappeared shortly thereafter.

3) I re-built the itinerary on united.com with a new record. I immediately called in to ask about confirming the EI flight. Got a US rep who also said it was unconfirmed, meaning unavailable. When I asked why it showed as available on the web site, she transferred me to web support. I waited for 20 minutes on hold and then got disconnected.

4) The record still showed the flights so I called a little later to try one more time. The US-based rep claimed 20 years of experience, but was not familiar with the EI booking. She was suspicious of whether 'U' was the correct fare class for an EI business award. After some research, she determined that it is. The then proceeded to "re-sell" the seat. The red text in my online itinerary was replaced by black text saying something else. Unfortunately, I failed to record either of theses messages. Early this morning, it ticketed.

That was easy!

I still wish that I know more about what happened, but here are my observations:
1) You WILL need human intervention. It may be best just to do the whole award on the phone, but if you do build it online, you MUST call!
2) Many of the reps, even experienced ones, are unfamiliar with EI award bookings. HUACA!
3) Don't count you chickens until they are ticketed!

I guess that these are pretty obvious bits of general FT wisdom and I let myself get a bit complacent when doing the original booking.

If anyone can shed more light on the process and the meaning of re-selling the seats, it might be helpful for other people, who will then be better equipped to hand-hold the UA phone reps.