If the date format is configured with Lower Case m's entered to signify the months (Example: d/mm/yyyy h:mm rather than d/MM/...) during the CSV import, the date displayed for the issues once imported will be incorrect:

Example: Using the following format: d/mm/yyyy h:mm with the date in the CSV file as follows: 29/May/08 - The actual date displayed for the issue will be: 29/Jan/08. For any date imported with this format the month will appear as Jan.

JIRA doesn't seen to be able to handle this very well -

JIRA should either allow this and recognise that if a Lower Case m is within a date it should recognise it as a month. Or, the import of these dates should fail and produce an error message stating that Upper Case is required. Rather than allowing the date to import and display it as Jan. Excel doesn't make this distinction allowing all lower case characters within date formats.