"n/a" instead of message when viewing message from user with different input format rights

When viewing a private message, in function theme_privatemsg_view($message), the module is calling check_markup check_markup($message->message, $message->format)

see:
http://api.drupal.org/api/4.7/function/check_markup

I think the proper call would include check=FALSE:
check_markup($message->message, $message->format, FALSE)

The reason why this matters:
If a user who has the rights to compose a message in full HTML does so to write a message to another user who only has the rights to compose messages in Filtered HTML, then that user will not see the message but only "n/a" instead.