asterisk users - Feb 2005 - TDM400P FXS works only if two lines are off hook?

I have a TDM400P with one FXO module and two FXS modules in it. I also 
have a Wildcard X101P.

After trying hard to get things working on various Intel computers, but 
having echo problems that made it not really usable, I decided to try it 
on some older PowerPC (Macintosh) hardware running Yellow Dog Linux.

Things started off smoothly. Both zaptel and asterisk seemed to compile 
okay, and both cards are detected:

kernel: Found a Wildcard FXO: Wildcard X101P
kernel: PCI: Enabling device 00:0f.0 (0004 -> 0007)
kernel: Freshmaker version: 63
kernel: Freshmaker passed register test
kernel: Module 0: Installed -- AUTO FXO (FCC mode)
kernel: Module 1: Installed -- AUTO FXS/DPO
kernel: Module 2: Installed -- AUTO FXS/DPO
kernel: Module 3: Not installed

I can dial out from a SIP phone through the FXO ports on the X101P or 
the TDM400P (with almost no echo), so some things are basically working.

However, the FXS lines didn't work properly: there is no audio in either 
direction. If I call these channels from a SIP phone, they do ring 
properly, and if I pick up a phone connected to them, the console 
correctly shows, for example:

   -- Starting simple switch on 'Zap/3-1'

But there is no dialtone and no voice audible in either direction when 
they are called. Outgoing calls from these FXS channels don't work; 
pressing numbers on the keypad beeps but has no other effect.

Then by accident I picked up both FXS lines at the same time, and both 
of them work perfectly! I get dialtones, I can dial and make calls with 
them, audio works in both directions -- nothing wrong at all.

So as long as they're both off the hook at the same time, everything is 
fine. But as soon as I hang up either one of the lines, the sound on the 
other line will *also* go dead again within a second.

A little more experimentation: having just one FXS module on the TDM400P 
(removing the other) doesn't work at all. The only way the FXS lines 
work is with both FXS modules installed and off hook simultaneously.

This problem occurs with the released versions (zaptel 1.0.4 with the 
wcfxs driver and asterisk 1.0.5), and with cvs head (using the wctdm 
driver).

Does anyone have any idea why this would happen, and how I could fix it?

-- 
Robert L Mathews, Tiger Technologies      http://www.tigertech.net/