The program shares a set of styles for use in all leagues. Each report that uses the same style number will appear the same for multiple leagues.
When changing a report style for a specific league, than all league using that style will change.
The solution is to select another style, and customize that style for that league. Example: Most leagues use the same style, such as #42. By using another style number, such as #44, for a different type of league, the regular league reports won't change.
See Changing Report Styles