User Agent Info in registration-cache

Hello Community,

I faced following strange behavior: user sends some special uri-parameter in Contact field when registers and SBC adds this parameter to the User-Agent Info in its registration-cache (a fragment is shown below). Why does SBC add this parameter only to INVITE requests sent towards actual user? All other consecutive requests within the same session (ACK, BYE, CANCEL) do not have this parameter in their request-lines.

  User Agent Info:

        Contact: sip:+74997100004@172.18.23.221:5060;uriparam=Test

        Realm: access-ims3

        IP: 172.18.23.221:5060

Thanks in advance!