Yup, pretty strange but then, maybe you don't let yours get as cold in fall/winter as Ursula or I do. I thought they were a type that has a dormant period in winter, and mine has always come back when the weather warms up in spring.
I guess you'd better hope that the people you've sold them to didn't have them go dormant and think they were dead, huh?
It would be a shame if they threw out a nice plant when it was "not dead, just resting" as Monty Python said . ..