If you answer the call from a Partner key phone, the 1A2 system will continue to ring a few times until the interrupter returns to the "parked" position.
This will result in two things:
The line lamps on the 1A2 sets will continue to flash, and then go dark. They will not stay lit through the duration of the call.
The common ringers (if wired through a local generator supply) will continue to ring about three times and then stop.
I cannot see any way to provide A-lead control to the 1A2 system when the Partner phones are in use, without some serious circuit design. You do NOT want to put a loop current detector in the line before the Partner, to give A-lead control to the 1A2 system, because it would interfere with a legitimate loop current closure from the 1A2 sets.
