As nobody answered this it might help to know that years ago when I was a child we acquired a paeony which did much the same thing. I seem to remember that this was something that does often happen with newly planted ones and it should correct itself in time. No way am I an expert or even grower of them - just fishing in my long term memory of childhood. Hope it encourages you to have patience anyway.

Thanks Stera, the individual flower was really beautiful but I shall hope for brothers and sisters next year!