we where able to reproduce the problem, the issue is a parameterized header that contains a comma character but no quotes around it. For example:
note that "Wed, 07" contains a delimiter character (the comma) but is not set into quotes. This leads to the reported error message - we assume a ; as delimiter character but , is read because quotes are missing. We're investigating if there is a possible workaround, from the technical side the E-Mail is not standards compliant, but i guess the recipient does not care about that stuff, he just wants to read his mail...
creation-date=Wed, 07 Jan 2009 17:29:20 GMT;
modification-date=Wed, 07 Jan 2009 17:25:27 GMT
thanks again for this report