Virtual Server will not deliver HTTP POST messages over certain sizes

What steps will reproduce the problem?
1. Using the router web admin application, go to NAT Setting -> Virtual Server 
and set virtual server for HTTP requests, forwarding port 80 to a local port on 
a PC from the LAN.
2. Send an HTTP POST message to the router's WAN IP address from the internet 
(not from the LAN!). The message must be larger than 3KB.

What is the expected output? What do you see instead?
Only the headers of the HTTP message will get to the destination server. The 
body will not. If the message has a small body size it will be delivered to the 
destination server without any problem. I don't exactly know the body size from 
which messages will not be delivered, but in my case this consistently happen 
on sizes above 3KB.

What version of the product are you using?
My router is an Asus WL-500 GP V2. I am using firmware 
"WL500gpv2-1.9.2.7-rtn-r4772.trx"

Please provide any additional information below.
The problem doesn't happen if sending the HTTP message to the WAN IP of the 
router but from a machine inside the router's LAN.

Original issue reported on code.google.com by dumitres...@gmail.com on 4 Feb 2013 at 7:04

hxping7 / wl500g

Virtual Server will not deliver HTTP POST messages over certain sizes #382