I will venture a guess here. GA's can be very busy and their time is tight trying to keep a flight on time, doing upgrades, rearranging seats etc. They are also not always fully trained to reissue tickets. I would think the issue is the DM line is at fault. They should have completed what had to be done (reissue the ticket or whatever). They have a bit more time and if they don't know how to do it, they can call a help desk. If they had told me to let the GA finish it, I would have insisted the DM agent complete it. Of course, there could have been other issues.