prevent 'Re: Re:' stacking

lib/controller/accountscontroller.php

@@ -231,7 +231,12 @@ class AccountsController extends Controller
 			$message = $mailbox->getMessage($messageId);
 
 			if (is_null($subject)) {
-				$headers['Subject'] = 'Re: ' . $message->getSubject();
+				// prevent 'Re: Re:' stacking
+				if(strcasecmp(substr($message->getSubject(), 0, 4), 'Re: ') === 0) {
+					$headers['Subject'] = $message->getSubject();
+				} else {
+					$headers['Subject'] = 'Re: ' . $message->getSubject();
+				}
 			}
 			$headers['In-Reply-To'] = $message->getMessageId();
 			if (is_null($to)) {