This is due to your Operating Systems "Separator Settings". For your reports to format correctly, this setting must be set to ",".
To do this, start by clicking on the Start Button (Windows Button), and then typing "Control Panel".
Open "Control Panel", and then select "Region".
A window will appear, and at the bottom of it will be "Additional Settings". Click on this button.
Another window will appear on the screen. Find the "List Separator" options and set it to ",".
Click "Apply" and then "OK".
Your reports will now format correctly in Excel.