Please describe the problem:
In some very specific circumstance described below, Evolution mailer inserts UTF8's BOM (=EF=BB=BF) 

This causes the resulting email to be rejected by some recipients (procmail...) because the resulting mail contain non plain-ascii text, even though the sender meant to send plain ascii file.

Steps to reproduce:
1. Click on Menu/File/New/New Mail Message
2. *Type* the exact text (don't press enter after "ddd") :
aaa bbb ccc
ddd
3. then select "bbb", copy it and paste it after "ddd".
4. then type eee
4. Save the message as a draft

Actual results:
If you reopen the draft, then open it, got to Menu/View/Message Source, you can notice that the message contains :

> Content-Type: text/plain; charset=UTF-8
> Content-Transfer-Encoding: quoted-printable
> 
> aaa bbb ccc
> ddd=EF=BB=BFbbbeee

Notice that :
A) There is the sequence "=EF=BB=BF" before the text we pasted.
B) The text is sent as  "Content-Type: text/plain; charset=UTF-8"

Expected results:
The content should have been :
> Content-Type: text/plain
> Content-Transfer-Encoding: 7bit
> 
> aaa bbb ccc
> dddbbbeee

Does this happen every time?
Yes, If the steps above are repeated exactly.

Note that the BOM is only inserted during the paste if the text is in "quoted-printable", not in "base64" encoding.

And 

The message is sent in "quoted-printable" if you follow the steps above (the constraints are :  The first line must contain at least three words, you can copy any of the three. The second line must contain at least 3 words, the pasted text must not be pasted at the beginning of that second line )

Other information: