Did you resolve this? I know it's a pretty stale thread, but maybe this will help you or the next person.
Static URL filter is slightly counter-intuitive and may not behave quite the way you expect. Please review documentation (for 5.4, see http://help.fortinet.com/fos50hlp/54/Content/FortiOS/fortigate-security-profiles-54/Web_Filter/Static%20URL%20Filter.htm). Pay close attention to the notes for Allow action. Allow passes the request on to other proxy functions, such as AV and Web Filter, so if the URL is in a blocked category, it will still be blocked. The Exempt action bypasses other proxy functions, and while this does prevent web filter from being applied, it also prevents AV scanning. A better solution may be to use web rating override to re-categorize a URL pattern from it's default Fortiguard category to another Fortiguard category or a custom category, then set that category action to the desired action.