Index: wp-includes/pluggable.php
===================================================================
--- wp-includes/pluggable.php	(revision 11557)
+++ wp-includes/pluggable.php	(working copy)
@@ -337,6 +337,12 @@
 		}
 	}
 
+	if ( !isset( $content_type ) || $content_type = 'text/plain' ) {
+		// Ensure we don't send encoded quotes in plain text emails
+		$subject = html_entity_decode( $subject, ENT_QUOTES );
+		$message = html_entity_decode( $message, ENT_QUOTES );
+	}
+
 	// Empty out the values that may be set
 	$phpmailer->ClearAddresses();
 	$phpmailer->ClearAllRecipients();