Do you have an example page with a menu on it where the slashes are applied randomly? The links that are created should be consistent depending on the values that you have for the root URLs.
Any page that is linked to with a / in front of it will be site relative where the / represents the root of the site. So if you have a link like this:
It will be assumed that this page is in the root of the site. If this page is actually in a sub folder it will not be found with a link like this.