Menu Designer: creating a menu item with both internal and external link value

1. in Menu designer, create a menu item
2. in "Link to", fill in the value for field: URL Design reference
3. also, fill in the value for field: External URL

Currently, HST site able to distinguish the internal/external link, however it needs to choose which link it should use.
For a user, the possibility to fill in both fields will result in confusion (since it can be that the HST prioritize over external link, instead of internal link).