Firewall/NAT

I have a server behind a Monowall (v. 1.32).  The client sends a TCP Keep Alive every 1 minute to keep the connection from dropping, however the response (ACK) is coming from the Monowall and not the server behind the firewall.  This is causing the connection from the server to the Monowall to drop at 2 hours (Windows TCPKeepAlive). 

With an inbound NAT is this expected?  I would think that the Monowall would pass the 1 byte TCP Keep Alive packet to the server and have it answer. 

Hiya, how comes you folks right here so wise and intelligent? I wish was born your brains guys (and girls). Yea, i'm sorry for off-topic, but I simply had to get this off of my soul. Keep up the good job everyone.