Same here... I feel like I'm stabbing in the dark with iptables sometimes. I switched from DD-WRT to OpenWRT earlier this year. I ran DD-WRT for years. OpenWRT starts to pay dividends when you have a USB on the router and can hang a large drive off of it.
Please let me know how you make out with this problem. If I find any additional info I will be sure to post it on this thread.