Exporting a portlet throws an error with invalid date range. Caused by:
1) Add document library portlet
2) Click on options (upper right of portlet) and select "Export/Import"
3) You can leave everything as default settings, just click "Export"
4) You should get an exception in the logs, which says: "Both start and end dates must have valid values or be null"
5) You will not be allowed to export the portlet.