Merge same address on export broken when user selects fields (instead of exporting primary fields)

Reproduced on demo site.

1. Export contacts and use a saved field mapping
2. Choose the 'Merge All Contacts With The Same Address" option
3. The resultant addressee and postal greeting simply states 'list of names'.
4. This doesn't happen with a primary fields export, only with a saved field mapping.

See attached screenshots and examples.