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 believe this relates to older versions of Safari. Because it is a Safari issue we can't fix it ourselves, but if you update Safari you should have no further problems.
Sorry for the hassle!