T48G - Outgoing call in progress drops on incoming call (35.72.0.10)

[tomp]

We tried 35.73.0.18 and this did not fix either I'm afraid.

2 users:

100
101

A ring group:

200

Containing users:
100
101

If user 100 rings 200 then I would expect both 100 and 101 to ring, however as soon as incoming call arrives at 100 phone, rather than call waiting, it hangs up the outbound call, which in turn stops the incoming call.