Why does a small change the in volume settings in WinMLS give no effect?

If the WinMLS mixer is calibrated (see Measurement->Calibration...), a change in the volume setting will always have an effect since the calibration procedure has determined the level steps that actually changes the level. However, if the mixer is not calibrated, the sound card level steps have not been determined, and slight changes in volume may not be supported. There should be at least 16 different levels and maximally 65535 levels of volume to choose from.