I think that you just had a combination of bad luck with agents and having bought up online on an employee fare. I've bought up on employee fares and made subsequent changes many times but ALWAYS through a phone call. The agent I spoke with always had to call to get the new pricing calculated and a new ticket reissued. The new ticket has been re-issued in the new fare class and is still categorized as an employee fare ticket. I've subsequently SDC'd changed tickets with no problem and no reference to 'original' fare class.