No, this is an incorrect and unfair statement. I've been flying Acro on Heli for years, never with an external FBL. I have never installed an external FBL or tail gyro on an Ardupilot powered system, ever. I've actually got a few that were given to me and/or came in kits that have never been installed. 1 SK720 and 3 Brain2's. (Available for sale if anybody wants them)
IMO, using an external FBL controller slaved underneath Ardupilot is a band-aid solution for an improperly mounted Pixhawk. And it really doesn't even solve the problem with the Pixhawk. You still risk crashing when the EKF blows up. The only thing it buys you is a fully "manual" bailout to rescue it... if and only if you have the piloting skills to fly the heli in rate only mode, from an unknown attitude, and possibly at great distance from the pilot.
As for the original topic... yeah... I don't know what's going on here. I will try to look into it. Eventually I will have to be flying on 3.4. I'm afraid that what that will look like, however, is a fork with a lot of cruft removed.