Server 2003 SP1 Firewall bug?

I ran into the following issue when applying server 2003 service pack 1 to
two of our web servers:

Our network configuration consists of network A connected to a firewall
connected to network B which is connected to the internet. Network A is the
"internal" network for our department and Network B is the campus-wide
network.

Both the web servers have two network cards, one NIC is connected to network
A and one NIC is connected to network B. All web traffic goes through the
network B NIC. The network A connection is only for snmp control of some
devices on the A network.

Before SP1: I had the ICF turned on for both network cards, and allowed port
80 through for the network B NIC. There were no incoming connections allowed
through the network A NIC. A computer on Network A was able to access the web
server just fine by going to the IP on the Network B NIC.

After SP1: A computer on Network A will not connect to the Network B NIC of
the web server (what used to work fine before) IF the firewall is enabled for
the Network A NIC. I do not see why the network A NIC or firewall should be
involved in the transaction at all. The Network B NIC does not have the
firewall enabled.
A check of the firewall log shows a

DROP TCP x.x.NET.B x.x.NET.A 80 4779 48 SA 2707667470 1137765220 16384 - - -
SEND

entry. I do not understand why the firewall would be blocking what appears
to be an outbound connection from the NET B NIC on the web server back to the
computer sitting on NET A? Disabling the NET A NIC on the web server fixes
the problem, so it does not seem like any traffic is actually traveling
through the NET A NIC, but the firewall on the NET A NIC is blocking traffic
traveling through the NET B NIC.

This all worked before the application of service pack 1. I am at a loss for
what could be causing this as far as a misconfiguration is concerned.