FTP/HTTP Connections thru Shorewall immediately disconnected

[Geoc]

Is there something in the Shorewall/Iptables/netfilter configuration we're not seeing which would cause connections to an ftp or http server be dropped immediately? Ethereal logs show a momentary successful connection, followed immediately by a disconnect by the host. Command line ftp shows the same thing happening, too.
This was (unsuccessfully) tested with the rules set to ACCEPT all traffic for all zones -- so the olde standbye (ping F.Q.D.N) works.