Autotune does not work with Navio

Does anybody know how to trigger Autotune on Navio+ ?

I set the channel 7 (also tried 8) in Mission Planner, I can see the radio signal switching to above 1800pwm but Navio will not switch into Autotune. I found a previous post from May 2015 where somebody had the same issue and an Emlid developer said they are looking into it but since then there is no more info on that issue.