For a few events it has been reported that the csv file doesn't open as a spreadsheet, but as a plain text file.
You can solve the problem by editing the file name.
The browser is adding .csv.html as the file extension. If you delete .html from the file name and re-open the file you will have a spreadsheet. ie revert the file extension to .csv which is what we generate.
We are investigating why this is happening as it is only occasionally. It may relate to older versions of Safari.
Sorry for the hassle!