Mine have been only angular ones from HDRshop, but I came to the same conclusion awhile ago and tested making mirror ball - it made no difference. The thing is off on the x axis by -90. My original all white HDRI came from Vue5 infinite, and it started life as a longitude HDRI. I generated the HDRI from a vue sky map with no clouds/haze/a white sky and the sun directly overhead. I think we're right here - Bryce has a bug. Go ahead and try making an Angular yourself after your render finishes. My testing showed they both were off.