[Serusers] HELP:could NOT account BYE/CANCEL messages with RADIUS

Hi,all I've tried to use RADIUS(freeradius-0.9.1) to account with SER(ser-0.9.3).But I can't account BYE or CANCEL messages,while I can account INVITE and ACK. In ser.cfg I write as follows: ... modparam("acc", "log_level", 4) modparam("acc", "radius_flag", 2) modparam("acc", "radius_missed_flag", 3) ... if (method=="INVITE") { log(1, "INVITE\n"); if (!radius_proxy_authorize("")) { proxy_challenge("", "0"); setflag(3); break; }; setflag(2); }; if (method=="BYE" || method=="CANCEL") { log (1, "BYE or CANCEL\n");\ setflag(2); }; ...

What's wrong with it?Is there anything I miss to configure? Please give me any hint and thanks a lot.