When a field on an edit form contains a foreign key value and the form is displayed as the detail form in a master/detail relationship, the field is rendered as readonly. This is fine and expected.
The problem is, if you're using a custom view tag, it ignores the custom view tag, since it's an edit form, not a view form. This results in inconsistent display of the field, when idisplayed on a view form vs readonly on an edit form. It's not practical to use the custom edit tag, since the field may need to be displayed as readonly when it's acting as a foreign key and editable otherwise.
When displaying a foreign key field on an edit form, PHPMaker should treat it as a view field, and format it according to the custom view tag, if one exists.