Yes Jim, I hear you and understand what you are saying. It is just that when trying to fix such problems it is best to start with a clean installation. I was providing justification for getting Mupi to that point.
So, starting from a clean MC23 installation, I don't believe MC has a bug. But it does have some quirks, and its volume control needs to be understood.
For example, if a user sets Volume Mode to Internal Volume, the System Volume slider and the MC Internal Volume slider act independently, and in an additive fashion. So 50% on each slider is actually 25% of the total volume available. If a user has set Internal Volume and has set Startup Volume to "-1" (which means leave the Internal Volume slider where it was last set when MC was closed), then when MC is launched both volume sliders are left at their last position. The System Volume slider because it hasn't been manually changed, and the Internal Volume slider because the Startup Volume hasn't been set to a specific value.
Now with those settings as soon as a user starts playing a media file, video or audio, the System Volume slider is set to 100% by MC, while the Internal Volume slider is left as it was. This is by design, because it allows the maximum volume output to the audio device, hence the best signal to noise ratio. Volume control is all done using the Internal Volume slider, although the System Volume slider can also be adjusted, and it will change the volume. When playback of the media file is stopped the System Volume slider reverts to the setting it was before playback started. So the System Volume isn't left at 100%, which would be a problem if any sounds were played outside of MC. As I am assuming WASAPI Exclusive mode output on the audio device (Realtek), then while MC is playing something no other sounds, such a system sounds, can be played. So no unexpected loud and potentially damaging noises are possible while the System Volume slider is set to 100%.
That is the way MC works and is by design. Note that if Volume Protection is turned on then when playback is started, the Internal Volume slider is set to 20% (if it was higher than that already) and movement of the slider is constrained so that a high volume can't be accidentally set with one click, for example. The Internal Volume slider is not set back to a position higher than 20% when playback stops.
Mupi, these are features that help protect your speakers from being overdriven by accident, when using the Internal Volume mode. Note that you can still control Internal Volume with your mouse. Just hover the mouse over the Internal Volume slider and scroll the mouse wheel. That still works on the System Volume slider as well, to reduce the volume from 100% where MC has set it.
So Mupi, you want to use System Volume slider in the Windows tray area to control volume, correct? Okay, I can understand that, even though Internal Volume mode is better. First, the setting we are talking about here is under;
Options > Audio > Volume > Volume mode.
So set that to System Volume, as you say you have done before. Now the System Volume slider in the Windows Tray area is linked to the volume slider inside MC. When either is set to 100%, the output volume will be maximised, and both will be the same %.
Again the volume slider will be left at their existing position until a media file is played, and then they will be set to 100%. Again, this is to maximise the Signal to Noise ratio output by your PC, so that your receiver/amp can make the best use of the signal. That is, your amp/receiver can be set at a relatively lower volume to get the same output, and with less noise from the source file. When playback is stopped the volume sliders are returned to their original position. Startup Volume and Volume Protection still work in this configuration.
But this configuration of MC isn't ideal, as when you finish playing something in MC the volume of other sounds from the PC are set at a lower level, and since the amp/receiver is set at a lower level, those other sounds, including for example playback of media files using other software, will be at a lower level than you want to listen to. Unless, of course, you always set your PC System Volume to 100% and control volume using your Amp/Receiver volume control. That is one of the reasons why Internal Volume mode is better than System Volume mode in MC.
But anyway, all that is academic and really just an education for you about how volume control works in MC. Hopefully, you understand more about the sophisticated volume control built into MC. If you still want to use System Volume mode in MC, and you do not want the volume to jump to something when you play a media file, go to:
Options > Audio > Audio Device > Device Settings > untick "Maximize device volume during playback".
Done. Fixed. There is no bug, just many settings in MC that need to be understood to get the best out of the software.
The only time I have seen the System Volume slider have no effect on volume output is when the WDM Driver is set as the default Audio Playback Device in Windows, and from memory, when Internal Volume is selected. In this case, the System Volume slider is trying to change the Input Volume to MC, via the Output Volume of the WDM Driver. This is not allowed because that would make the signal to noise ratio worse. Hence why I suggested uninstalling the WDM Driver, to remove the possibility that you have been trying to use MC in that way.