OpenWRT: No internet access from clients but the router

I run OpenWRT 8.09rc1 on an ASUS WL-500gp. After adding some advanced rules to the firewall in luci I recognized some problems on my clients with the internet access. The connection to the router via ssh and http was no problem. The router was able to connect to the internet. Seems like some routing problems. I changed nothing huge expect some small firewall rules which should not affect this. I was not able to fix this by stop/restart the firewall. After trying several hours and searching the net for some information I found this thread.

The clients could access the internet again after running this:

echo "0" > /proc/sys/net/ipv4/tcp_window_scaling

It seems like there are some problems with the firewall script. The script changes some settings on startup and does not revert them when stopping. I turned of that firewall script to use my own now for these things.

Btw. I was able to search the net from my client by adding a dynamic tunnel to my ssh connection with the router and adding a socks proxy to my browser.