Symptoms
There is custom Order Notification Template specified in Home > System > Settings > Notifications > Common Notification Settings, but a different notification is sent on sales order placemenet.
Cause
An issue is caused by the bug with id #PBA-29868 ("Change of the Order Notification Template does not have any effect").
Resolution
Change the notification template (TemplateName) used in the MESSAGE handler signature:
Home > System > Settings > Events > Event Type Order Placed > Event Handlers > MESSAGE::OrderNotification