The work around that we are currently doing and so far is the easiest is to:

click on email invoice (quote, statement, ect) and when the email pulls up for editing in outlook just save and close it.  Then go into Outlook and open the draft and do the necessary edits and changes and then send.  This seems to be working for my office. Of course you should test it to make sure it works for you since some solutions work for some users and not others.

It is by far the simplest work around solution that we have found to date.   

I do hope this gets a resolution in the future, but I am just grateful we have something that works for now.  

Good Luck!