Symptoms
Changing the content type of any email notification template, e.g. "Send link for change password" from text/html to text/plain, doesn't persist after OSS Core service (pau) restart. It always gets reset to 'text/plain'.
Cause
Odin Automation sofware issue FND-2978.
Resolution
There is no workaround to avoid the behavior. The only workaround is to change the content type manually at System > Settings > System Notifications > Email Templates > Send link for change password.
Contact TAM or PTA Team to request a hotfix for the software issue.