One of the things that calibration (auto or manual) attempts to do is find reference level for your system. That means zero dB on the volume knob should equal 85 dB at your listening position, no matter what combination of speakers, amplification, room gain, etc, that you have.
As such, it has to override your current volume setting each and every time you calibrate. Keep in mind that things such as Loudness Compensation are set based on where reference level is.
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Sanjay