RTL chipset & multicast bug?

I’ve been trying to get multicast datagrams with network cards that uses RTL8139# chipset, in some cases it work fine, but in other cases I can’t get anything (it looks like depends of the multicast address).

I made the tests in QNX 4.25, datagrams from some multicast groups were read perfectly, but other ones couldn’t be reached never (not even with a netsniff). The solution was change the network cards, 3com cards didn’t give me that problem.

Now I’m using QNX 6.3, and I have the same “bug”, some groups are reached an others not… I change the network card and it works fine, does anyboby know why this happens?

P.S. I have tested whith intel and corman network cards too, these ones didn’t give me problems.