If you are still fighting with this and you're trying to add multiple values to that one field check out the Aggregating multiple values into single fields section of Importing data from CSV:
You can import multiple values into a single JIRA field that accepts multiple values (e.g. Fix (for) Version, Affects Version, Component, Labels). To do this, your CSV file must specify the same column name for each value you wish to import to the same field. The number of column names specified must match the maximum number of values to be aggregated into the mapped field.
IssueType, Summary, FixVersion, FixVersion, FixVersion, Component, Component
bug, "First issue", v1, , , Component1,
bug, "Second issue", v2, , , Component1, Component2
bug, "Third issue", v1, v2, v3, Component1,
In the above example, the Component field of the second issue and the Fix Version field of the third issue will generate multiple values in the relevant field after importing.