The reason for the error message is that the calibration functions were primarily designed for direct-emitting speakers.
However, as soon as dipole speakers are utilised, error messages can occur due to the spatial playback, because the dipole concurrently emits both phasings - the correct one and "the wrong one".
The reason why one speaker is displayed as "correct" and the other one as "incorrect" polarity is because the sound is reflected variably due to the spatial conditions and consequently arrives variably at the measurement microphone. Depending on which proportion of the sound is recognised by the microphone first, the receiver then decides whether there is (an assumed) false polarity or not.
Because polarity is visible based on the pole clamp markings on the speakers, you may ignore the measurement of the receiver.