Zone Contaminant Source or Sink CO2 Gain seems to be wrong

In my multizone Energyplus model with AFN I have no gas equipment and the Carbon Dioxide Generation Rate in the people schedule in every zone is set to 0. The only CO2 sources are ZoneContaminantSourceAndSink:Carbondioxide objects.(1 in every zone)

While the output variable values from "Contaminant Source or Sink CO2 Gain Volume Flow Rate" correspond to the input schedule (right y-axis) in the "ZoneContaminantSourceAndSink:Carbondioxide" object, the "Zone Contaminant Source or Sink CO2 Gain" (left y-axis) doesn't correspond to anything. Shouldn't it be the same as the Contaminant Source or Sink CO2 Gain Volume Flow Rate? (Because there are no other sources in the zone)

Is this expected behavior or am I missing something?

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Following code snippet shows how these output variables are calculated

    for ( Loop = 1; Loop <= TotCO2Gen; ++Loop ) {
        NZ = ZoneCO2Gen( Loop ).ZonePtr;
        ZoneCO2Gen( Loop ).CO2GainRate = ZoneCO2Gen( Loop ).CO2DesignRate * GetCurrentScheduleValue( ZoneCO2Gen( Loop ).SchedPtr );
        ZnRpt( NZ ).CO2Rate += ZoneCO2Gen( Loop ).CO2GainRate;
    }

where ZnRpt( ).CO2Rate = Zone Contaminant Source or Sink CO2 Gain Volume Flow Rate [m3/s] and ZoneCO2Gen( ).CO2GainRate = Contaminant Source or Sink CO2 Gain Volume Flow Rate [m3/s]

Reporting during warmup convergence for timestep frequency would verify that ZoneCO2Gen( ).CO2GainRate is design generation rate multiplied by schedule value. And ZnRpt( ).CO2Rate is the sum of ZoneCO2Gen( ).CO2GainRate in successive timesteps. Also, above code doesn't take into account inputs from People or GasEquipment objects. So even if CO2 inputs in these objects are changed, it should not make any difference into above output variables.Agree though that documentation for the variables is confusing.