[Serusers] radius accounting

[SER Users]

hello, 

I have ser configured with radius accounting and for each call
I get two Start packets and one Stop packet. 

Is this the correct behaviour or I have miss-configured something ?
The only difference between the two Start Packets is the "Sip-Method"
attribute which in one is "Invite" and in the other one is "Bye" 

In my configuration I have: 

...
modparam("acc", "radius_flag", 2)
modparam("acc", "radius_missed_flag", 3)
...
setflag(2);
if (!t_relay()) {
  sl_reply_error();
};
... 


thanks,
Razvan Radu