I would capture packet traces of SIP from FS->PBX under 1.0.6 and 1.2 and compare those here.

On 18 January 2013 15:20, support@ecn.net.au <support@ecn.net.au> wrote:
Again the start_dtmf issues exists only in 1.2 and 1.3 FS , in the 1.0.6 the issue is not present (is this a bug possibly?)