FOSS gamedev and creative worlds

When I was mining, I noticed that my minimap seems to change based on my current elevation. When standing at my base, the minimap shows the overworld/ground level. However, when I get deep enough, the minimap changes to show what I assume is supposed to be underground or something. Is this known/expected behavior? I haven't found any documentation about it.

Here's a two image imgur album that shows what I'm talking about: https://imgur.com/a/XiP56

The minimap shows a top-down view of the terrain from 126 meters above your current elevation iirc.

the surface mode shows the top layer of the world in vision range.
when you are underground, it doesn't show the things you see on screen.

for that is radar mode, it highlights air green and leaves the rest blank.
the brightness of the green shows how close it is to you.