All users from that website?
Only Notes users from that website?
Only Notes 9.0 users from that website?
Only Notes 9.0 users on Windows 8 from that website?
If you open up the same email, from the same users mail file, on a different PC do you still see it there? If so, maybe they have a check mark on that user that says something different, like use a special formatting. Years ago I did have to contact a customer and ask them to change a setting.