Even after you disable caching, the previous CSS may still be cached in your browser.
You need to go away from your site then clear the browser cache then come back to your site. If your site is active in the browser when you clear the browser cache it will not clear it for active sites in the browser.
Then once the cache is cleared it should not cache it while you have caching disabled, but it was already cached in your browser before you changed the settings.
Hope that helps,
Joe