This is Google Translate.
In “Brush Presets”, tags other than All and All Untagged do not show that the brush presets have been changed.
Trigger method:
Switch to “Ink” Tag.
Adjust the opacity of “Brush Presets”.
It is found that the icon does not show that it has been changed.
This is the normal display of the icon that has been changed.
Maybe it’s a translation problem and I just don’t understand your description.
I have never noticed a change in the icons there, it is after all a setting that you always adjust when painting. Sometimes you have more, sometimes you have less “paint on the brush”.
I did your test with version b347ab1, but neither with “Ink” nor with “All” nor with “All Untagged”, I didn’t notice any changes of the icons when I changed the value for “Opacity”, I hope it’s not because of my old monitor and it can’t show the changes anymore, because they are too small.
Michelist
The changed/dirty icon is supposed to be shown and it is shown when using 4.4.5 for all of the tags when the opacity, size or blending mode value is changed.
The Jun 30 5.0.0-prealpha has the problem as described by @Eranthis_stellata
Was it said that the many and various 5.0.0 problems would be reported in the forum here for some kind of summary analysis?
It’s the sort of thing that needs a bug report but we can ask @tiar
How inattentive of me, I never consciously noticed this as a result of a change and always thought it was a normal part of the icon that I thought some had and others did not. I also only noticed it now when I looked at the icon while moving the slider. That “this little black dot” has this function was unknown to me. Thanks, so I learned something again! 
Michelist
This is Google Translate.
Because my English is too poor, I need a lot of pictures to help explain.
Then I posted it here.
I do it exactly the same way, as pictures are often very helpful I like to use them for support. And my English is not so good anymore (Edit: like my eyes) and I check my texts mostly with DeepL and Google Translate, and still I am not always understood. But you seem to enjoy participating here as much as I do and that’s what matters.
Michelist
