When selecting 'Reports > Participation report' in a Moodle course you can't change the 'Show actions' select box to filter only view/post participation for an activity.
The following code (/course/report/participation/index.php) always evaluates to false, resetting the $action variable:
$actionoptions = array('' => $strallactions,
'view' => $strview,
'post' => $strpost,);
if (!in_array($action, $actionoptions))
Changing the in_array test to use array_keys($actionoptions) allows you to filter different actions