Hovas,
I think you are looking at your problem the wrong way. If the POTS lines are pointed directly at a CRA then there are no timers that will affect the call because it is already answered and playing a message.
As for what your problem is I would say it is a form of "Talk-Off" that is at play here.
Could you post how you have your digit translations set up?
Also show us your DTMF Detection Timers to see if there were any changes to the some of the twist values.
Can we assume this has been working properly for awhile now or is this a new application?
Have you tested your POTS lines for abnormal conditions (noise, static, voltage, etc..).
If you point them to a different CRA do you have the same problem?
If you put in a different recording, ie rerecord the message on a different recording number and use that, does it do the same thing?
Thanks,
TE