My office is having the same issue.  Our invoice email template recently changed on its own and is full of errors and gimicks like "hope to see you again soon" which are not any part of our template.

We have been on the phone with QB support for more than 6 hours over two days with the problem ongoing for over a week now.  We cannot send any invoices by email because they are embarassing and disrespectful for our industry.  This is a software issue although QB support keeps telling us to make a new template that we are doing something wrong.

QB needs to get software engineering on this problem for everyone it is not a user error!!!