asterisk users - Jul 2005 - double dtmf in incoming SIP call?

Hi,

I have a problem with DTMF in incoming SIP call (from pstn2voip provider).
Every phone keypress is detected by asterisk as doublepress (I
press 1 and get 11).
I connect to pstn2voip provider by SIP, allow only alaw codec.
dtmfmode=inbound.

After pressing '1' while asterisk executes WaitExten command,
in the full log I get:
DEBUG[25492]: Launching 'WaitExten'
VERBOSE[25492]: -- Executing WaitExten("SIP/a.b.c.d-0814f820",
"5") in new stack
DEBUG[25492]: Sending dtmf: 49 (1), at a.b.c.d
DEBUG[25492]: Oooh, got something to jump out with ('1')!
DEBUG[25492]: Sending dtmf: 49 (1), at a.b.c.d
a.b.c.d = IP address of my pstn2voip provider 

Any ideas?

Best regards,
-- 
Bart