Problem sending mail with parentheses in the subject

[Grenty]

Hi,
I am using the latest version of prestashop and am having an issue where I am unable to send email when the subject
has parentheses in it. In addition, I have tracked it down to where it appears to only have problems when there are 6 or more letters between the parentheses.

For example, when sending emails with subjects:

MyProduct (abcd) - works
MyProduct (abcde) - works
MyProduct (abcdef) - does NOT work
MyProduct (abcdefg) - does NOT work
etc.

I have tested this using the contact forms and the send to a friend to a friend feature with the same results.

I have been unable to figure out what is going on. I do know everything looks acceptable until the end of the Swift::send function where these calls do not succeed.

$send_event->setNumSent($sent);
$this->notifyListeners($send_event, "SendListener");

Does anyone know what could be causing the problem?

Thank you very much for any help or suggestions!