I get round this problem by adding an additional field which is a numeric ID, 1,2,3 etc and attach this to the values that I am using as categories. You can then sort the data by the numeric field in the chart data source query and the text catogories are then in the correct order.
I usually use a separate table for this so any changes are easy to make and then link the category text field in this table to the category text field in the main data source table.
Regards,
Alain