I have tried this with designer 2.1 and 3.0M2.

Quite often the data we use in Mapping Tables consists of cells of CSV

i.e this is a row of one table I have with the first column being a DN

CN=E5,ou=D4,ou=C1,ou=B1,ou=DHS,o=Org-Structure o256 Respite DHS
Disability Services Division

If I export this table from Excell to CSV and import to a Mapping
Table it loads correctly.

If I export this table from an exisiting mapping to CSV and import to
another Mapping Table it automatically uses the commas in the DN as
delimiters and therefore the first column will be divided into 6

I have noticed the export from Designer encloses each cell in
quotation marks whilst Excell does not.