Dial *8 -> pickup outgoing call

Many times when i dial *8 to pickup an incoming call ringing on a near by phone and somebody else dials 9 xxxxxxxxxx to place an outgoing call the asterisk ( Trixbox ) connects the two phones together and the incomming call steel ringing .
Did any one had a same or similar experience like this ?
Any sugestions to trace or fix the problem
Asterisk Version 1.4.19-1
Trixbox Version stable

Thanks in advance