When I export a number of defects from QC (9.0) to excel the date format for the 'detected on' field sets itself to a different format. However this only happens for some of the defects, not all of them and I cant work out why?

For example there is a defect detected on 12/05/2011 in QC, but in excel it will display as 05/12/2011. But then there is also a defect detected on 20/05/2011 in QC and this remains the same in excel.

Ive noticed that in excel if you reformat the cell to English (United States) it shows correctly, but this is not possible to do the lot in one go, cause some are displayed correctly.

Anyone have any ideas?