NAT Type Strict or Moderate since update

Hi, ever since the update (not the recent one a few days ago, the one a couple of weeks or so ago) when I go onto Black Ops Online my NAT type is either Strict or Moderate. However, if I 'Test Xbox Live Connection' it tells me that it is Strict or Moderate and to restart my router. I do this and 95% of the time it works and then my NAT Type is then Open until I switch off my Xbox and go back on it I have to do this again. This is rather annoying now and I this has only been like this since the Update on Black Ops the other week. I've set up a 'Static IP' for my 360 but this has made no difference at all. Just wondering if anyone else is having the same problem, or did have and know how to solve it completely?

Thanks

andyronnie