asterisk users - Oct 2013 - DTMF detection problem with analog card

Hi all.
I have a DTMF detection problem by my new analog card (ATCOM 2 FXO port).
When i`m playing a voice with 'GET DATA' AGI command, sometimes asterisk
do not receive DTMF from caller while the voice is playing. But if user waits to
the end of playing voice, there is no problem.

I`m using Asterisk 10.3.1, dahdi-2.6.1 on CentOS.6.4.
Could you please help me?
Here is my configs:

system.conf:
----------------
fxsks=1
fxsks=2
loadzone??? = nl
defaultzone??? = nl

chan_dahdi.conf:
----------------------
[channels]
;==============;General options
;==============usecallerid = yes
hidecallerid = no
busydetect=yes
busycount=3

;==============;FXO Modules
;==============group = 1
signalling = fxs_ks
context = my-context
channel = 1,2
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