contacts export - saved field mapping does not persist 4th column selection

When attempting to create or update an export field mapping that involves having a 4th colum, such as
Individual -> Phone -> Home -> Mobile
The last column of information (in this case the "Mobile" selection) is not correctly stored and/or recalled as part of the field mapping.
This requires a manual process be performed to reselect the appropriate 4th column field (i.e. "Mobile") before an export can be done even with an existing field mapping.