I'm not quite sure why you're using words like "incorrect", su_, given the evidence of native speakers in this thread.If a group of people pronounce a word incorrectly, and teach this to their children , should this incorrect pronunciation be considered as correct?
A hypothesis. The h is pronounced in this word in correct AE, so we have to say "a". Now I have heard a few Americans drop the h in this word (and a few others like human being, historical analysis etc.) and then they would say "an" in conversation but I don't think you should imitate this, and never in written AE. But this is just what I would do.