Comment 12 for bug 266166

In comment #9 above, 815297 is a Sourceforge bug number. The issue in launchpad is https://bugs.launchpad.net/mailman/+bug/265967

Regarding comment #11 and Mailman 3, Mailman 3 uses Python 3 and the email package, which is the source of this issue, has been almost completely rewritten for Python 3. One of the goals of the rewrite was to make the result of parsing/flattening match the original text, so I suspect this is fixed in MM 3, but I'm not certain.