iptables+nat+Tcp KeepAlive Problem

Hi List!, I'm having some issue with iptables when I use DNAT. Using DNAT, when my router (iptables) gets a tcp KeepAlive Packet from remote site, it don't forward the tcp KeepAlive Request and responds with a TCP packet with ACK=1 and RST=1. So remote site thinks that there is no connection after some time. The problem is only with KeepAlive Packets, If I send normal Tcp Packets with data, they arrive to the destination I used in DNAT.

Any help or idea of where start looking? Iptables support Tcp KeepAlive redirects?

iptables version: v1.4.1.1
Kernel: 2.6.28-11-generic

iptable rule:
iptables -t nat -A PREROUTING -p tcp --dport 5555 -j DNAT --to-destination 192.168.1.100

Wireshark TCP Packets:
186449 11772.258110 200.49.201.26=>172.16.102.11 TCP [TCP ZeroWindow] [TCP Keep-Alive] 14032 > 5555 [] Seq=10 Win=0 Len=0
188417 11835.763745 172.16.102.11=>200.49.201.26 TCP 5555 > 48538 [RST, ACK] Seq=1012825070 Ack=10 Win=0 Len=0

Thanks and Regards.