Issue on FAX enabled on Inbound PSTN route

My environemt is this:

Trixbos 2.6.0
Freepbx recently upgrader to 2.5.1
Asterisk 1.4.18-3

My issue is this:

I’d like to enable fax service on an inbound PSTN line.
The PSTN line is not dedicated to fax reception but is normally used to place and receive calls.
For this purpose I’ve setted in:

General Setting:

and on inbound route (i.e. on a Zaptel Channel):
Fax extension: FreePBX Default
Fax Email:
Fax Detection Type: NVFax or Zaptel
Pause After Answer: 3 (or 6, or any other value)

By this way I can receive fax that are e-mailed correctly but if the inbound calling is not a fax the extensions (added to the ring group setted as “destination” in inbound route) continue to ring even if the caller (another phone and not a fax) has hunged up.
The phone continue to ring until a person (uman) pick the handset and, obviously, hear nothing.
Is there any way to resolve the issue ?
In other words can I use the same PSTN line to receive and place call on a PSTN line and at the same time use the PSTN number as an automatic fax receiver?
Thanks in advance.

Ing. Cosimo MERCURO
Mercuro for Busines