10.0.1 has a very impressive list of fixes. I think I understand them all except maybe for one.
I have no idea what that means. If it’s People List View, then it sorts on the column you click. And what is the primary fact that People List displays and sorts on?
It’s probably pretty obvious, but I can’t figure it out.
I have not yet installed v10, but my layman’s reading is that:
One can display a Fact-type column and then Sort on that column. Whereupon, the Fact-type which is marked Primary is used when more than one of that Fact-type happens to exist (ie. two different Birth dates or Birth places can have (only) 1 marked as Primary). Am I right? 
Aha! I’m sure you are correct.
Wow! certainly does! one of the longest list I remember in using RM for over 3 years.