I have no idea why this doesn't work, but none of my custom button actions (tasks) do anything in my component. In my view.html.php file I have:
JToolBarHelper::custom('reports.export_csv', 'csv', '', 'CSV', false);
JToolBarHelper::custom('reports.export_mailchimp', 'mailchimp', '', 'Mailchimp', false);
Then in my ReportsControllerReports file I have 2 methods (not just 2, there are some others but they aren't relevant), export_csv() and export_mailchimp(). Whenever I click the buttons I get a JS error which I assume is preventing the action from executing the code in those methods. Something about "b is undefined". I cannot find any differences between my code and that used in other Joomla (core) components, so if anyone could shed some light on this issue it would be greatly appreciated (as usual, the Joomla forums are totally useless).