Netflow through a mapped ip address on a Netscreen firewall

Hello,

I have Netflow installed and running on over a hundred router - I love it!

But, our Internet router is behind a Netscreen firewall.

Internal Address of Netflow is 10.10.10.10
I have mapped the internal address to an external address on the firewall.

My internet router points to the mapped IP address of the Netflow server. It works fine for an hour or two then just stops recieving flows.

I can get it working again by disabling the rule on the Netscreen firewall that allows the traffic through, then re-enabling it.

Have you seen or heard of this type of behavior before?

Thanks