This section of the forum is intended for reporting possibile software bugs. No need to repost, but if you had posted this in the FM Pro Forum (See tab at top of this screen), it would have been seen by more people and have gotten a faster response.
It sounds like you are attempting to add fields after specifyng a table occurrence that is not related to the layout's table occurrence or that of a portal if you are adding the fields to a portal row. Table occurrences are the "boxes" found in manage | database | relationships. When you select a 'table' from the drop down at the top of the specify fields dialog, you are actually selecting one of these table occurrences. If you select one that isn't related and then add fields, you are adding fields from an "unrelated table" and you get that indication on your layout.