there is a way to work in a mirror way with a bone .....(
Here my steps:
create a biped guide (for human body) ; in this step i'm able to work in mirror mode
Rig from biped guide
Set envelope and assign the rig to the body: now i can't able to work in a mirror way....
P.s. I've checked the mirror and pose constraints, and chek the SYM button, but does'nt work for me..