Strange Behavior with TFTP process

[mcarey]

Server A tftp's to Server B
Both Servers are behind R55p firewalls and have allow any rules to each subnet

The TFTP process fails. In the log, I see a seperate datastream start from Server B to Server A on a high port above 5000 and the traffic gets blocked.

Server C tftp's to Server B
Both servers are behind R55p firewalls, but Server C is running on a different CMA and allow rules to each subnet are in place with ANY service just like the 1st situation

The TFTP works successfully and I never see a 2nd data stream initiated from Server B to Server C like I do in the 1st situation. This is what I except a TFTP stream to look like.

The only way to get Server A to TFTP properly to Server B is to place a rule between Server B and Server A in the firewall directly in front of Server B with the ANY service allow?

This doesn't make any sense....any ideas?