There should be an additional right in 'Roles and Permissions' - 'Issue Tracking' with the name e.g. 'View related issues'. If this is activated all users with this role can view all related issues independant if they have rights in the project where the related issue belong to. If they have no rights, the issue number isn´t a link.

We have a lot of issues which are related to other issues with the relation 'blocked by'. But if users haven´t the rights on both projects they can´t see the relations and so e.g. they don´t know why it is no possible to close an issue.