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

If the WinMLS mixer is calibrated (see Measurement->Hardware Calibration...), a change in the volume setting will always have an effect since the calibration procedure has detected the level steps. However, if the mixer is not calibrated, the sound card level steps have not been detected, 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.