The dropdowns for adding a relation (like adding an issue to a person) do not exclude all the existing issue relations if you are looking at the second page of issue-relations in the subform.
Ex. if a person has 25 issues connected to them, and is looking at the second issue subform page - the dropdown list won't exclude the issues that are listed on their first page. Thus it's possible that a user will try to add the same issue twice - and get an error message. It also messes up the view a little.