I have had this issue when sorting the legend in an Excel Chart. It
will not sort my values ascending although it is listed as ascending in
the series order tab of the "Format Data Series" option. It is so
frustrating. I have to go the Series Order tab and then move them into
a descending fashion so that it will sort ascending. I am confused as
to why it keeps doing that. My original list is ascending as well, so
it does not makes sense. Any clues on why it's doing this or how to
fix it? THANKS!

Example:
Here's a simplified version of what I'm talking about. This is my
list:
Business
Financial
Private

In the Excel chart, it shows up as:
Private
Financial
Business

Also, sometimes the legend is all out of order and the sort doesn't
make any sense, such as:
Financial
Business
Private