Maybe this isn't a cache problem, but I am using Drupal 6, I have cache disable and I am editing a custom nice menu CSS file.  

I didn't see changes right away to my nice menus, so I cleared the cache in the performance page, and the menu would revert back to old changes. When I cleared the cache again, it randomly found new settings for Nice Menu.  
I then installed Devel, and cleared the cache, but it didn't help. Clearing the browser cache didn't help either.

Do you have any idea?