received short dtmf result in endless dtmf to sip about asterisk-chan-dongle HOT 2 OPEN

if you want just pass DTMF directly to other leg of channel just say dtmf=off.
this mean inband DTMF still, but no detection DTMF by asterisk at all.

logic for cut short DTMF not perfect, but can your offer other solution?
cut DTMF begin and wait for DTMF end ? Whan passing DTMF up from chan_dongle?

the major problems for asterisk DTMF detection is duplicated DTMF and
asterisk do actions (for AVR ) on END edge of DTMF 

With dtmf=off you can't run a menu system in asterisk, so that wouldn't help 
much. (Not that I'm planning on using that, but chan_dongle should support it.)

Properly detecting and handling inband DTMF is one of the worst things to do 
right, especially with GSM channels that can randomly drop a few frames...
For some applications, length of DTMF digits is not relevant but inter-digit 
time is. For some other applications, the length is relevant, but inter-digit 
time is not. Trying to get both right is almost a mission impossible. 
(Heisenberg compensator, anyone? :-) )

I'll try to dig through asterisk sources and see if I can think of something. 
This is a very promising project (potentially saving our customers lots of 
money spent on expensive simboxes) and I'd be happy to help and improve it!