tftp helper not working

I've got a number of routers whose management interfaces sit behind a 200D.  There is a tftp server on the public side.  I added a rule that permits them to reach outbound to the tftp server using tftp as the service.  The tftp helper appears to be present:

edit 5 set name tftp set protocol 17 set port 69 next

tcpdump on the tftp server shows the write request reaching it, and it sending data back from a random high port to a random high port, but the return traffic never makes it back to the router through the 200D.

Is there something additional I need to do to allow the helper to work?