Sppedtouch 716 router - firewall information/documentation

I have a Speedtouch 716WL router which works very reliably.

Recently I had an issue where a remote Fedora Core 6 client wouldn't
talk with my Slackware system which is behind the Speedtouch router.
(All other remote systems I tried were fine BTW).

The issue turned out to be that the Speedtouch firewall was not
sending packets back to the FC6 system because of its TCP sequence
checking, the error reported was:-

FIREWALL fast tcp seqnr check (1 of 2): Protocol: TCP Src ip:
192.168.1.1 Src port: 22 Dst ip: 193.128.168.194 Dst port: 51097

Disabling the check fixed the problem.

However I'd like to know more about the Speedtouch firewall and the
checks it does, the documentation simply tells you how to set/clear
the checks and nothing about what they actually do or what they
protect against. (This is the Speedtouch CLI document)

Is there anywhere that tells me more be it web based, a document or
whatever?

--
Chris Green