WebI Document Date columns get exported to Excel as Text

Good afternoon

I have the following problem.

I created a document which is based on a Universe. Such a Universe contains some date - time columns. Within the WebI document I use a function called FormatDate in order to show these column's values in "MM/dd/yyyy" format, as follows

However when I export the report to Excel or Excel 2007 the column's value come out as Text on the Excel file generated:

I'd expect the value generated in Excel to have a Date format instead of Text, but I don't really know why is this behavior happening

I'm using SAP BO 4.0 SP 10 Patch 01.

Thanks for your comments