You are right, the flowers are very similar but the leaves are different. I looked on Google, looks like Z. is not fully hardy, when P. is; although they are both alpine. I do like your plant, I'll try to find it in the UK. I'll make more photos of P. next season. Now my rockery is covered by double fleece (frost protection).
It's a beautiful plant like a piece of jewellery. I have it in my rockery. I moved it in 2012 and it performed well. Tiny steams are like pine tree needles, little red flowers are amazingly bright caching your eyes from distance. I've never cut it back in early spring as it's required. I may try this year.