i know that there are some Chromatic Aberrations on the HPX171 but at my last outdoor shoot i was really shocked when i saw these purple color shifts. I know it was a pretty extreme situation but is this normal? Or ist there a way I can avoid this?
Almost certainly lens flare, a hot white sky with a darkish subject will always burn out , look at the way the detail of the branches in the same area has gone. All electronic cameras will do it, the HPX handles it pretty well. I've seen similar things shooting birds against overcast sky
Only real solution is to keep the sky out of the shot, or at least away from your subject then no one will notice
Make sure your filters are clean and scratch free to minimise flare, apart from that you could shoot on film or bring in a couple of 10k's...
I know that this was a pretty extreme situation, that i will loose detail and could expect some blue color shifts (CC) there. But i often shoot against bright sky with my HPX but i never saw such extreme purple shifts before.