The work around for this is to change the line (210) from:
$theMailerMime->setTxtBody(stripForText($mailBody));
to
$theMailerMime->setTxtBody($mailBody);
This issue was logged in our bug base, but we were not able to reproduce it. Could you tell me any additional information about your mail set up or UE set up that help up us in reproducing this issue. The part of the code is related to the body text, so any information about the body text should be helpful.