OK - just to record the fix for this -
The specific issue was that inbound calls were not recorded in the station's missed call log -if- the call rolled to audix. If the call dropped prior to going to audix, it was logged.
This occurred only on 9640G and 9608 stations; 4610 stations worked normally.
The solution was to add SET LOGUNSEEN 1 to the 46xxsettings.txt file.
## LOGUNSEEN specifies whether incoming calls that did not cause alerting will be logged
## as missed calls (e.g., calls that are forwarded because the phone is busy).
## Value Operation
## 0 Unseen calls will not be logged (default)
## 1 Unseen calls will be logged
## This parameter is supported by:
## 96x1 H.323 R6.0 and later software releases.
## 96x0 H.323 R3.0 and later software releases.
SET LOGUNSEEN 1