forward first and fallback not working

[marco at nucleus.it]

Hi,
bind 9.10.3_p4 with this global option:

forward first;

forwarders {
   8.8.8.8;
};

If i dig from localhost or any client and 8.8.8.8 answers all is ok but
if 8.8.8.8 is unreachable or it doesn't respond, bind doesn't fallback
on himslef asking to root server etc .

This is not expected.
Anyone with this behavior ?

best regards
Marco