COS blocks Queue Callbacks in rare situations

Witnessed on client pbx where Queue Callbacks and COS are enabled. When the system places the outbound call to an external DID for callback, for some reason the Asterisk function CALLERID(number) is null for this call. When the callback call attempts to bridge into the Queue, first the cid macro is called, and you can see there is no CID:

[2016-09-07 08:36:29] VERBOSE[13995][C-0003686f] pbx.c:     -- Executing [s@macro-user-callerid:1] Set("Local/920xxxxxxx@queuecallback-2-00048fe4;1", "TOUCH_MONITOR=1473255375.887865") in new stack
[2016-09-07 08:36:29] VERBOSE[13995][C-0003686f] pbx.c:     -- Executing [s@macro-user-callerid:2] Set("Local/920xxxxxxx@queuecallback-2-00048fe4;1", "AMPUSER=") in new stack
[2016-09-07 08:36:29] VERBOSE[13995][C-0003686f] pbx.c:     -- Executing [s@macro-user-callerid:3] GotoIf("Local/920xxxxxxx@queuecallback-2-00048fe4;1", "0?report") in new stack
[2016-09-07 08:36:29] VERBOSE[13995][C-0003686f] pbx.c:     -- Executing [s@macro-user-callerid:4] ExecIf("Local/920xxxxxxx@queuecallback-2-00048fe4;1", "1?Set(REALCALLERIDNUM=)") in new stack
[2016-09-07 08:36:29] VERBOSE[13995][C-0003686f] pbx.c:     -- Executing [s@macro-user-callerid:5] Set("Local/920xxxxxxx@queuecallback-2-00048fe4;1", "AMPUSER=") in new stack
[2016-09-07 08:36:29] VERBOSE[13995][C-0003686f] pbx.c:     -- Executing [s@macro-user-callerid:6] GotoIf("Local/920xxxxxxx@queuecallback-2-00048fe4;1", "0?limit") in new stack
[2016-09-07 08:36:29] VERBOSE[13995][C-0003686f] pbx.c:     -- Executing [s@macro-user-callerid:7] Set("Local/920xxxxxxx@queuecallback-2-00048fe4;1", "AMPUSERCIDNAME=") in new stack

Then the COS check fails with:

[2016-09-07 08:36:30] VERBOSE[13995][C-0003686f] res_agi.c:  cos.agi: Starting Class Of Service checks
[2016-09-07 08:36:30] VERBOSE[13995][C-0003686f] res_agi.c:  cos.agi: CallerID not Parseable - received unknown - exiting with DENY