Asterisk is picking the flash signal from external zap trunk

Is there anyway to make trixbox ignore the ‘flash’ signal from an external extension?

When a call is transfered using the ‘flash’ button from an external zap extension I can hear the music on hold, but it never goes away!

The call is transfered and the person on the other side of the line can hear me, but all I hear it’s the music on hold.

thank you!