it's an issue from the cdr, I think. There is another post I wrote, to investigate on this problem. You colud find it mdt-daniel, it's a post of these days. According to the last replies, the problem arises when trunks have the "insecure" parameter, because this parameter lets asterisk use only the ip address of voip server to register, and ignoring the account datas (user and password).
I ignore how a trunk can be registered without check and use the account credential, but this is what we could read about the "insecure" parameter.
There are lot of thinks I ignore about voip sip, even if I use it (and set up atas and pbxes for years), and I already noticed that there are very understandable settings that may or may not involve in any situation.