Combined vs. Division results

Why in some cases in IPSC/USPSA (Hit Factor scoring) the Combined results come in a different order of finish comparing with Division results?
The short answer is that stage points are based on the stage winners in the division.  When looking at combined scores those winners change so the stage points change.
Long answer follows:
This happens in any points scoring system where the points are scaled to the best score.

Example:

Stage 1:
Pam gets an unusually low score on Stage 1 for her division. A 15 percent disadvantage, below Rosie. That is 19 percent of Doug, the division winner for the stage. They are all in Limited.
Bob is shooting Open. Bob blows them all away. Doug who won limited is only 16.66 percent of Bob. Rosie is 16.13 percent of Bob. Pam is 13.51 percent of Bob, but that is only a 3 point disadvantage below Rosie. So in the combined results, in relative terms, the Limited shooters are all really close.

On all other stages they Pam and Rosie run neck in neck but Pam comes in just ahead of Rosie.
Now look at the overall results. First combined. Pam beat Rosie because Rosie’s advantage on stage one was negated by Bob’s performance relative to all Limited shooters.

Now look at the Division resultsRosie beats Pam because the advantage he had on stage one is huge relative to the division they are in. This despite Pam beating him on every other stage.