Call-ID is mandatory on all SIP requests. Asterisk found that it was not present in the request when preparing the response (it could have also been when constructing a related request (re-invite or BYE), but one would have expected to get this error on the initial response.
Although the function returns an error status, that is ignored, so the response will be sent without a Call-ID.
The requesting party should not be able to match the response with its request, but then it was badly broken not to send Call-ID in the first place, so all bets are off.
Based on a lightly dated branch version of Asterisk 1.8, as you didn’t provide an exact version
asterisk-dominicana*CLI> core show version
Asterisk 11.11.0 built by root @ asterisk-dominicana.com on a x86_64 running Linux on 2014-08-09 21:56:15 UTC