asterisk users - Oct 2009 - Missing digits from CallerID on TDM400P?

I have a TDM400P hooked up to an analog line from KPN in The 
Netherlands. CallerID is working but sometimes some digits are missing 
from the number, i.e. if the number that calls me is:
0204569236

I will sometimes get this in the display:
020456236

Which digit is missing seems to be fairly random. Where / how could i 
start debugging this ?

This is my etc/dahdi/system.conf :
fxoks=1
echocanceller=mg2,1
fxsks=4
echocanceller=mg2,4

loadzone        = nl
defaultzone     = nl


This is my /etc/asterisk/chan_dahdi.conf :
echocancel=yes
echocancelwhenbridged=yes
echotraining=400

callerid=202
signalling=fxo_ks
group=1
context=intern-all
channel=>1

signalling=fxs_ks
cidsignalling=dtmf
cidstart=polarity
usecallerid=yes
callerid=asreceived
hidecallerid=no
callwaiting=no
callwaitingcallerid=no
group=2
context=inbound-analog
channel=>4


Thanks!
Remco