Dial goes to next context (voicemail) during active call


Anybody had a similar experience or can recommend anything?

Context calls a macro
Macro uses Dial to make a SIP call with the rgoM options
The Macro passed by Dial does not return anything so bridging should be successful
The next line in the context routes to voicemail (if Dial is unanswered)

What happens:
A call is made using SIP to several numbers and Dial successfully rings the phones
The call is answered on one of the phones using a SIP channel
Talking for several minutes on successful call
Suddenly the called party cannot hear the caller but the caller can hear the called party
After a few seconds the called party is disconnected
The caller is then routed to voicemail (next context as if call was unanswered)

Verbose Asterisk shows the two calls packet-to-packet bridging correctly
[Talking on successful call]
There is no hangup for the called party - nothing is logged when we suddenly can’t hear each other (if they hung up I would not be able to hear them saying Hello?)
The next line in the context is called during the active bridged call as if the call had never been answered
This results in voicemail being connected (because it is the next line in the context)

Asterisk 1.1.12

Any ideas?