Bad header breaks confirmation mail function – duplicate MIME field

Event Registration 6.00.31
Plugin code is adding duplicate MIME-Version field to mail header.
Flagged as bad header by Amavis and mail is quarantined, not sent.
Breaks registration confirmation e-mail functionality.

Current working fix in my install:
Commented out
$headers = “MIME-Version: 1.0\r\n”;
and changed the following line to be an initial string instead of a concat string in following relevant files:

…/wordpress/wp-content/plugins/event-registration
# find . -type f -print | xargs grep MIME-Version
./lang/en_US.po:”MIME-Version: 1.0\n”
Binary file ./lang/default.mo matches
Binary file ./lang/en_US.mo matches
./lang/default.po:”MIME-Version: 1.0\n”
./evr_support_functions.php: $headers = “MIME-Version: 1.0\r\n”;
./payments/evr_admin_payments-post.php: $headers = “MIME-Version: 1.0\r\n”;
./payments/evr_admin_payments-case.php: $headers = “MIME-Version: 1.0\r\n”;
./payments/evr_admin_payments-update.php: $headers = “MIME-Version: 1.0\r\n”;
./public/evr_public-process_confirmation.php: $headers = “MIME-Version: 1.0\r\n”;
./public/evr_public-process_confirmation.php: $headers = “MIME-Version: 1.0\r\n”;
./public/evr_public-process_registration.php: $headers = “MIME-Version: 1.0\r\n”;

Don’t know if this will break something else – not yet in my install.
Any developer comments welcome.

Example bad header (irrelevant bits removed):
—————-
…
X-Amavis-Alert: BAD HEADER SECTION Duplicate header field: “MIME-Version”
X-Spam-Flag: NO
X-Spam-Score: 0
X-Spam-Level:
X-Spam-Status: No, score=x tag=-9999 tag2=6.33 kill=6.33 tests=[]
autolearn=unavailable
…
Message-ID: <[email protected]>
X-Priority: 3
X-Mailer: PHPMailer 5.2.1 (https://code.google.com/a/apache-extras.org/p/phpmailer/)
MIME-Version: 1.0
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Content-Type: text/html; charset=”UTF-8″
Duplicate header field: “MIME-Version”
———————-

https://www.ads-software.com/extend/plugins/event-registration/