Export as XLS is not working correctly - dates change half way thru the file

Export as XLS is not working correctly - dates change half way thru the file

Dear Sirs,
From today when I export as XLS in Creator the format of the file changes half way.
The date values come as numbers and this issue is giving me problems while updating my files on zoho reports and also when I download the file to keep my local database up to date.
I am attatching a sample file that I've just exported and you can see that it suddenly changes all dates to numbers.
This is probably due to a current update you have made to your system.
Please let me know if this has a solution.
Best Regards,
Denis Shrosbree