The reply-to header isn't working.

I have some php mail generated with an reply-to header. But when I reply this e-mail its sent to the original sender, not to the e-mail listed in reply-to header, why?
Via gmail, it works well and the e-mail is sent to the address listed in reply-to header, but from eMClient don’t.

I have the same problem. Please reply.

My header:

Received: …Date: …
To: to@server.com
From: Admin <a@myserver.com>
Reply-To: User <b@myserver.com>
Subject: Help
Message-ID: …
X-Mailer: PHPMailer 5.2.16 (https://github.com/PHPMailer/PHPMailer)
MIME-Version: 1.0

Facing same issue in version 7 and its really annoying. Reply-To header is supported by all email clients, in fact it was working in version 6 but stopped working in latest version.

any word on this being fixed?