Hi louptech, just wanted to tell you that you're not alone. I have an IONITX-G-E and I'm experiencing the same symptoms and resolving it in the same way as you. Unfortunately, due to my chassis I can't even install a PCIE NIC to use instead. I'm stuck with this guy. Luckily, it's more of an annoyance than a big problem, because once it begins working it continues to work until the next powercycle. I would be more upset if it randomly flaked out during operation. I copied 2 terabytes over the network to it (it's hosting my new storage box), so I'm pretty sure the NIC is reliable once you kick it the right way!
Have you tried the machine in Windows? I suspect something's just wrong with forcedeth.