No DTMF detection on Asterisk originated zap outbound calls

I have a callback application that creates a call file and drops it into the
/var/spool/asterisk/outgoing directory. This file places a call and
goes to a DISA context when the call has been answered.

This works perfectly over SIP phones but does not work on my ISDN PRIs
(neither Digium TE210P nor TE205P card) both connected
to german t-com e1 (in Germany called S2M) trunks.

If I dial IN to the same context, DTMF is detected fine but if Asterisk originates the call, DTMF is not recognized.

This happens on all phones that receive calls (not only mobile phones).
One strange thing here:
On 1 of about 20 tries DTMF recognition works fine when Asterisk dials out.
In this case I can see the debug message

Jul 9 16:58:29 NOTICE[3871]: channel.c:2424 __ast_request_and_dial: Don’t know what to do with control frame 15

When this message appears DTMF tones will be detected

I’m using all latest versions from digium

all compiled and running on a HP Proliant 3GHz Xeon Server with
Debian Sarge and Kernel 2.6.8-3-686-smp i686

Things I have already tried that did not solve the problem until now:

  • changed relaxdtmf to yes and no in /etc/asterisk/zapata.conf
  • changed callprogress=no to yes in /etc/asterisk/zapata.conf
  • changed ‘static int vpmdtmfsupport = 1;’ to ‘0;’ in /usr/src/zaptel-1.2.6/wct4xxp.c and then
    recompile zaptel drivers and asterisk (like mentioned in digium kb)
  • using a own context with background() and WaitExten() instead of DISA Application

In Newsgroups and the internet I also can’t find any problem solution for that
(you will find some problem descriptions with the same problem but no solution for that)

Does anyone have the same problem or anyone have ideas how to solve this issue?

Thanks a lot,