I have a native ninebark (seed grown) and it reached flowering size this spring and had quite a few. But what baffles me is that literature describes it as flowering on old wood, and I noticed today open flower clusters and many more coming at the terminal ends of new growth.

Having not grown ninebark but once before (perhaps 20 yrs ago), I don't remember this happening. I know that lots of spring flowering things can get semi-confused and throw some autumn flowers.