One of its parents, Dryas octopetala (assuming I'm getting that right?), has an extended bloom season in the wild here where I see it, and tends to repeat through the season in the garden. So, while I haven't grown D. x suendermannii, I could imagine it might get that from D. octopetala.
What is the other parent supposed to be? I was under the impression it was D. drummondii... could that be right? Isn't that what led to a bunch of misinfo about "nodding flowers" and what not?