Let’s say you have the url http://my.site.com/myfolder/mypage.aspx#hash and you want to use it as a link into your left navigation bar in Sharepoint…. If you try putting that name, Sharepoint will not keep your link.
The trick here is to add a questionmark juste before the #. The URL to use will be http://my.site.com/myfolder/mypage.aspx?#hash and Sharepoint will accept the link 🙂