I had a look at the code now and this is actually a bug. When you call spjs.dffs.processEmailTemplate it will trigger a save after the email is sent.
It was not supposed to do that when you manually triggered an email, but I usually do that in DispForm so I haven’t noticed the form being saved (this will of course not happen when in DispForm).
I’ll address this issue in the next release.
PS: If you want to send the email when the form is saved – and not immediately when they click the button – you can call this function instead:
spjs.dffs.handleEmailTemplate("TemplateID", true);
Alexander