[Serusers] exec module question

[Andres]

Hi,

I am testing the exec module by outputting some variables to a flat file 
using:   SIP_HF_<hf_name>

So for example I put something like 

exec_msg("echo `date` - From: $SIP_HF_FROM To: $SIP_HF_TO  Contact: 
$SIP_HF_CONTACT Src_IP: $SIP_SRCIP User-Agent: $SIP_HF_USER-AGENT >> 
/var/log/ser/ser_register.log");

but the User-Agent header field does not get passed even though a sniffer 
trace shows it in the SIP REGISTER request.

Can somebody tell me why not?

Thanks,
Andres