asterisk users - Dec 2003 - X100 (when the phone line is not functional) and TDM400

Hi,

I have a small configuration with an X100P, one TDM400 (4 lines) and about
10 soft phones (DIAX).
It works perfect for more than one month now.
Yesterday the POTS phone line was deffective (no power).
Then I have seen some strange behaviour.
When someone tries to call a PSTN number(from TDM400 or DIAX), one of the
other extensions rings.

This is what I have in the extensions.conf file for the PSTN numbers:

[pstnlocal]
exten => _[23467]XXXXXX,1,Dial(${GROUP1}/${EXTEN})
exten => _[23467]XXXXXX,2,Hangup
exten => _[23467]XXXXXX,102,Hangup

How this is possible?
How the X100P card interpret power missing on the PSTN line?

Thanks,
Dan