Last year (before the UA/CO merger) I looked at the seat selection page for a LHR-IAD flight with E+, and for some reason, there was one row of E- within the E+ section, so I selected a seat there to see what would happen. A few days later, that row was back as E+, but I kept the seat and had it for the flight.

Were the extra leg room seats appearing like normal seats or you just weren't charged for them?