After an event at the weekend, I batch updated all 'pending due to pay later' participants to 'attended'. It appears that this triggered the re-sending of the confirmation email to all those people. Does anyone know why this might have occurred and how to avoid it in the future? We're using CiviCRM 4.6.3.
In my CiviCRM experience, this does indeed happen. CiviCRM seems to expect participants to be Registered before they are Attended. If you try to skip this step in the bulk update, it will move them to registered and trigger the email. Have a look at those participants and see if their status is now Registered.
We ensure that the are moved from the pending status to registered prior to the event as this also ensures that they get the registered email confirmation which they won't have received if they were still pending.
This (unfortunately) is expected behaviour when you have enabled Online Registration => Confirmation Email in the Event Configuration page.
This Issue Tracker thread is relevant though: https://issues.civicrm.org/jira/browse/CRM-12277
My interpretation of that is that some notification was supposed to be added back in 4.3 letting the user know that emails would be sent when you attempt to batch update status via profiles.
it is indeed intended behaviour and happens, when the class of a participant status (e.g. from pending to positive) changes. You can check your participant status here: yoururl.org/civicrm/admin/participant_status?reset=1
Good news is: There is an extension that prevents sending out the emails. As with all new functions, please test properly (if possible on a test environmet) before using it with live data :)
Actually what I wrote below is not correct. It was based on the linked Question, but my experience since indicates that emails do in fact still go out with batch changes.
It is also possible to change multiple participant statuses using the Update Multiple Participants action with a profile that includes the Status. In this case, only statuses changed from Not-Counted to Counted (or vice versa) have confirmation emails triggered (assuming Send Confirmation Email is enabled for the event).