Hi @Gunar Funke
Have you tried the dates in full format with matching masks (your dates and masks as posted don't match at all)?
e.g. 30/02/2012 10:19 with a date mask of dd/MM/yyyy hh:mm
Please take a look at the second question of this article: https://confluence.atlassian.com/display/JIRA/Commonly+Asked+CSV+Questions+and+Known+Issues
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