Problem with encoding in Freeradius

[biuro at globeinphotos.com]

Hi
To be honest I do not know is it really problem with encoding.
We integrate OpenSer with Radius and during INVITE phase Freeradius receives:
        Digest-User-Name = "test001"
        Digest-Realm = "test.pl"
        Digest-Nonce = "44be69da8b019499f882d3422d4e80e54a457bee"
        Digest-URI = "sip:+48580001 at test.pl"
        Digest-Method = "INVITE"

Digest URI contains "sip:+48580001 at test.pl" which is value typed by user.
But few lines below sql statement is called but this time Digest URI has
incorrect value:

test.authorize_reply('test001 at test.pl',
'sip:=2B48580001 at test.pl', 'INVITE' )'

'+' character was converted to hexadecimal representation.

Do you know why this conversion happen? And how to switch off this conversion.

Regards
Michal Szymanski