This has been a sore spot with all developers and it still isn't fixed. Data loss bug : Spontaneous and erroneous import matching of new fields in specified imports !
There are no work-arounds except that every time you add a field to a table, you must open all import scripts which write to that table and see if any of them spontaneously mapped. It still angers me that FM has known about it for YEARS. It causes us all major problems; over-writing data, wiping out important global data used to set relationships and so forth, and many people using FM aren't even aware of the dangers (that you've just discovered).
If, at any time, you add a field to a table and an import's external source has more fields than your table, it will happen. Very bad.
The only exception to this, and it may not apply to your situation, is if the two tables have matching field names such as when you import from a back up or for some types of file upgrades. In these cases, the matching names option in your import matching will prevent the misalignment.
That's nice when you can do it, but not possible when you have to align fields with differing names.:smileymad:
Thank you for your post.
As LaRetta mentioned, this problem has been reported previously and our Development and Software Quality Assurance (Testing) departments are aware of this issue. I have attached your post to this case. Until this is changed, be aware of this issue when you start adding fields to your database structure.