The guide didn't understand that I was going to Phnom Phenn and returning to Saigon by plane and getting a visa on arrival at the airport. Although I showed him my letter of invitation from Immigration department and plane ticket on Qatar airlines.
He left me with others returning to Saigon after getting their visa stamped.
Eventually he understood what I was doing and had to go my motorcycle from the boarder to the restaurants where the bus was stopped for passengers to eat and have comfort break...
I had 5 minutes to go to WC and get a cold drink. Not enough time to eat.