Yeah, that happened to me about once or twice a year at the fill station in the warehouse parking lot dive site that was in those days known as Dutch Springs. Once each year's batch of summer exchange students pressed into service as fill station attendants was made aware that Trimix 1 is a superset of Nitrox, all was cool until the next season.That has happened to me as well. I'm sure it wasn't uncommon when trimix wasn't as broadly advertised outside of technical diving.
Fortunately, another employee arrived and resolved it before i left.