I booked a IAD-DEN trip about a month ago for a trip on August 3. The return flight had R space available for upgrade with miles, but not the outbound flight. So I tried the waitlist. Today the outbound upgrade cleared.

I had been under the (clearly mistaken) impression that if R space is not available for domestic flights at the time of booking, then it is never released. I guess that previously I had been unable to figure out the upgrade waitlist procedure, after they changed the reservation system.

Just like with the old reservation system, I had to call United to have the reservation agent "clean up" the reservation.

FWIW, the flight still shows R0.