Cisco 7940 missed calls message on group dial

It is not an issue, rather a question.
Say we have a group dial like Dial(SIP/12&SIP/13&SIP/14)
Say 12 answers the call.
13 and 14 get a “missed call” on their Cisco 7940s.
This is logical, while phones “do not know” that somebody else answered this call.
But customer complains that previously, with their old Alcatel switch for the group calls, missed call message was displayed for non-answered calls only.
They claim that Microsoft new baby OCS also handles such situations OK.

Is there any solution workaround for the described scenario?
They have Cisco phones with SIP firmware

any comments welcome