asterisk users - Feb 2016 - Asterisk 13.6.0: ChannelDtmfReceived message generated twice towards the ARI application

I have an ARI application that is registered for Stasis in the dialplan.
One of the events I reap in my application is a ChannelDtmfReceived. The
thing is, Asterisk 13.6.0 sends me two DTMF for each DTMF pressed (have
tried both SIP phones and landlines). That is, I receive two
ChannelDtmfReceived for each DTMF pressed. Is there a configuration I
should try?

Specifically, I received these DTMF over a PSTN via a SIP trunk.

Here's what I see when I RTFM the problem (in
/usr/local/src/asterisk-13.6.0/configs/samples/pjsip.conf.sample):

;dtmf_mode=rfc4733      ; DTMF mode (default: "rfc4733")

it then means I don't have to set this anywhere!

What am I missing?

Any insight is appreciated.
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