General :: Odd Bug With BPF Filters On FC/Dell Hardware?

I have a FC12 OS installed on a Dell PE1850. I am setting up a snort/tcpdump sniffer interface on eth1.This is typically a very simple process - but I ran into something really funky. When I a generic tcpdump or snort dump on eth1, I see all the traffic I expect to see. I see dst 80, dst 443, dst 445 etc.However, as soon as I specify any BPF filters, it only shows applicable "src" traffic. (Ie I see a.a.a.a -> b.b.b.b:80, but none of the return - only the outbound.) If I remove the filter, its there again, all the bidirectional traffic. The same things applies when running the snort command. I can see both directions on a basic snort dump - but once I apply any BPF filters, I see either only source or nothing at all. My BPF syntax is correct.