Sharing an incoming line between * and another device

Should this be able to work?

One of our phone lines has a distinctive ring number which is used for our fax. I was have too much trouble getting rxfax to work so for now I decided to simply hook the fax machine directly to the incoming phone line. However, I split it so Asterisk could still use the line (it’s also part of the hunt group for our main number).

Incoming calls work fine. Distinctive rings are detected by the fax machine and answered while I have Asterisk configured to detect it and do nothing. Normally calls are answered properly by *.

The problem is that when someone attempts to send a fax from here Asterisk will for some reason think a call is coming in and answer it. Most times the fax manages to go through but it’s pretty annoying to have the extensions ringing whenever someone sends a fax.

Does anyone know why it would do this and maybe how I can prevent it?

I’m running 1.2.13 of Asterisk and I’m using a pair of X100P FXO cards.