I think I have it:
link text
Confirmed this on a 1810G-24 GE, using the last firmware (P.2.22 at this time). The “Auto DoS” feature blocks NFS : ip packets come in, but never come out from the switch.
And to notice : disabling the feature is not sufficient to make it work again. I had to do a hard factory reset (factory reset from the web gui did nothing) to make it work again.
It seems that this option is stickying somewhere in the configuration, even after disabling it !

