Go to Monitoring -> Events. If you have more events than what can be fit into the first page then when you use "Export to CSV" only those events that fit the first page are exported. This makes the CVS export useless for most cases.

If you look the form of the "Export to CSV" button it clearly shows that there's a "page_csv" property which tells which page it should export. I'm not sure if this is intended to be a feature but it clearly breaks UX in this case.