What is the meaning of the vertical indicator bar location in Custom Programs?

In the Starkey app, I am aware that saving a change in a Professional program only lasts for the duration of while that program is set. Saving a change for a Custom program modifies that program for all time. Fine.

I accidentally discovered that if the volume is not at the 50 level when you save it, then it seems to adjust the gain for that program (and even the balance if you have adjusted the volume independently). This was unexpected.

I still don’t understand how this works. And I find that I sometimes have to delete the custom program and start again to go back to normal volume. Can someone explain it a bit more?

There is also odd visual feedback. The “midpoint” volume bar gets moved. For example look at this. What is it telling me exactly?