Enigmail Breaks TB Charset-Encoding Prefs?

[auctoris]

=Short Version=

Enigmail ignores the "label as ASCII when using only ASCII" pref and disables the "for messages that contain 8-bit characters, use 'quoted printable'" every time I send an encrypted message. How do I make it stop?

=Long version=

I have Enigmail set to use ASCII armor so the cyphertext is always ASCII. ISO-8859-1 is my default character set and I have the "label as ASCII when using only ASCII" pref turned on. I also have the "for messages that contain 8-bit characters, use 'quoted printable'" pref turned on.

If I send a plaintext message, TB correctly sends it using the character set "US-ASCII" and content-transfer-encoding "7-bit". If I encrypt a message with Enigmail (ASCII armor on), Enigmail sends the message using the ISO-8859-1 character set and "8bit" content-transfer-encoding.

The cyphertext is just ASCII text. Why isn't Enigmail letting TB use the "US-ASCII" character set as my preferences dictate. Also, since the cyphertext only contains ASCII, why is it not using "7-bit" content-transfer-encoding? *And* why is it disabling my quoted printable prefs and using "8bit" (even though there are no 8 bit characters)? When it does this, I have to manually reset that pref every time I want to send a plaintext message as quoted printable.

If I cut and paste the cyphertext into a new message, TB will send the message using my correct preferences ("US-ASCII", "7-bit"). The cyphertext is received and decrypted perfectly.

Is this an Enigmail bug? Why is it changing character sets and transfer encodings when there is no need for it? How do I make it stop?

Thanks