IAX Speex issues

Hi there,
I am trying to tweak my Asterisk servers to talk to each other using Speex codec.
I downloaded and installed speex and speex devel libraries, recompiled asterisk (including make clean), did set up speex codec as only one allowed on both sides. Sounds enough.
However, conversations are not Speex encoded!!! It is codec 64 (ADPCM I believe) all the time.
Any clue as to why Asterisk don’t want to kick in Speex into play?

Any help is welcome.