On my StarAliance round the world trips in paid BUSINESS-CLASS UA names the class "D".

On transatlantic - transpacific - South American UA-flights (and on all three-class-aircrafts systemwide) I sit in comfirmed business and I am credited the 25%-business-class-bonus. On UA-two-class-flights I sit in comfirmed first with a 50%-class-mileage-bonus (not only for flights in continental USA and Canada, also to Mexico and Puerto Rico).

(one exception which will hit me on my Hawaii-party-flight in Nov-99: for the West Coast - Hawaii-segment the UA-rules do downgrade "B"-class to eco: my UA-people in Frankfurt tell me, that this is the only segment systemwide, where "B"-class is automatically downgraded).