Report Date in UK format as downloaded, but whenever the user change the date, it changes to US format i.e. MM/DD/YYYY.
Reproducing the Issue
You download ORD report as XLSX with UK date format DD/MM/YYYY, Right click on the date cell > Format Cell > Locate (location) English (US)
Now change the date in the cell / example 31/12/9999 to 10/12/2016 - type enter - the date default to US format : 12/10/2016
The Excel default date format is US MM/DD/YYYY, whenever you make change even though the date was in UK format will change to US format.
EXcel default date format Date Format US date format , KBA , LOD-SF-ANA , Analytics & Reporting (Ad Hoc, YouCalc, ORD) , Problem