Copter-3.4-rc5 available for beta testing

PixRacer compass

I updated a 250 quad racer from APM micro to Hobbyking PixRacer with external Micro HKPilot GPS And Compass u-Blox NEO-6 and HMC5883.
To have wifi module workable I updated from 3.3.3 to 3.4 RC4 and now RC5.MP 1.3.40/41

The copter flies great with default PIDs, no wobbling on high speed (Flight modes: stabilized, loiter, alt hold, pos hold). There is only one issue: when I activate more than one compass it is necessary to calibrate compasses nearly before every flight.
Post Idea for reducing frustration with compass prearm failures confirms this problem.

One of 8 testflights was interupted by an EKF2 error and failsafe land with only the external compass activated.

Is there a way to solve this?