Zaphfc / NT-mode / group Dial / busy problem

I have 2 HFC cards running NT mode, with 2 phones connected to each.
Individual internal dialing works fine.

However - if I issue a group Dial command to 2 phones on the same interface,
(type/identifier separated by ‘&’ e.g. Dial(Zap/g1/202&Zap/g1/203)),
then - if the first listed phone (202) is busy - the other one won’t ring either.
If the second phone (203) is busy - then the first one will ring.

If a pick up 200 and call a group consisting of all 4 phones
( Dial(zap/g0/200&zap/g0/201&zap/g1/202&zap/g1/203) )
then of course 200 is busy so 201 won’t ring either, but both phones on zap/g1 will ring.

There seems to be kind of a sequential bail-out on a per-interface basis.
If the first phone is busy, the entire interface is considered busy?

Is this an issue with the zap channel, or the zaphfc driver ?
Or is there anything I could do in my dialplan to avoid this?

regards
Torgrim

2 phones on 1 channel would work just like 2 phones on the same pots line in a house if 1 phone is in use the line is busy and I dont see a way around it

He is talking about ISDN, so there are 2 B-channels per line, the setup should work the way he is expecting.

@torgrimg
It looks like a configuration problem. A D-channel trace of the call setup could be helpful. You can get that by doing ‘pri debug span x’ on the Asterisk CLI.

If you lift both Handsets on g1, do you get dialtone on both of them?