[quote user="idw"]RFC 2047 is the proper one here, and I'm too lazy to elaborate, sorry.[/quote]
OK - did not read all relevant. [:$] May be this (from chapter 6.2) is the relevant paragraph:
   Decoding and display of encoded-words occurs *after* a
   structured field body is parsed into tokens.  It is therefore
   possible to hide 'special' characters in encoded-words which, when
   displayed, will be indistinguishable from 'special' characters in the
   surrounding text.  For this and other reasons, it is NOT generally
   possible to translate a message header containing 'encoded-word's to
   an unencoded form which can be parsed by an RFC 822 mail reader.
If I don't missunderstand. in our example with encoded comma the mailclient should be aware, that decoded comma is a special character due to RFC822 and has to be masked or addressheaders have to be handled in a way, that using for creating a mail (i.e. by answering) will not result in unwanted addressing of mails.
 
        
<p>[quote user="idw"]<a href="http://www.rfc-editor.org/cgi-bin/rfcdoctype.pl?loc=RFC&amp;letsgo=2047&amp;type=http&amp;file_format=txt" mce_href="http://www.rfc-editor.org/cgi-bin/rfcdoctype.pl?loc=RFC&amp;letsgo=2047&amp;type=http&amp;file_format=txt" target="_blank">RFC 2047</a> is the proper one here, and I'm too lazy to elaborate, sorry.[/quote]</p>
<p>OK - did not read all relevant. [:$] May be this (from chapter 6.2) is the relevant paragraph:</p>
<pre>   Decoding and display of encoded-words occurs *after* a
   structured field body is parsed into tokens.  It is therefore
   possible to hide 'special' characters in encoded-words which, when
   displayed, will be indistinguishable from 'special' characters in the
   surrounding text.  For this and other reasons, it is NOT generally
   possible to translate a message header containing 'encoded-word's to
   an unencoded form which can be parsed by an RFC 822 mail reader.</pre>
<p>If I don't missunderstand. in our example with encoded comma the mailclient should be aware, that decoded comma is a special character due to RFC822 and has to be masked or addressheaders have to be handled in a way, that using for creating a mail (i.e. by answering) will not result in unwanted addressing of mails.
</p>