It seems to be an et4000 related problem. I heard from several users that they have this problem. But not all et4000 have this problem. Perhaps you can add a script in runlevel 3 which restarts network automatically. Something like
ifdown eth0
ifup eth0
Yes, look like a PHY problem. I don't think there is a good solution for that other than what betacentauri says.
This is exactly what i was thinking.
this is probably an error in the pcb layout whit the mac controller, or the chip is bugged.
I think i'll open the chassis to check the revision of the pcb and compare it with other owners of et4000.
In the meantime i'll try to make a script that ping the network and restart the interface if it's down.
Thank you all, cu for updates