That’s an interesting one, I was able to replicate it.
I don’t have an authoritative answer for you (maybe someone else does), but I can guess.
My two cents…
A couple of characteristics for an “inline block” is that they layout horizontally and wrap to the next line.
So think of writing text in a word editor. When your sentence gets to the right edge of the word editors screen, it automatically wraps to the next line.
In your scenario, you set the height of the section less than the height of its child elements. Since inline block layouts out horizontally (much like text in a word editor) it wrapped to the next line (overflowing) - which is outside of its parent.
I could confirm this even more by setting the sections overflow to hidden. That clipped it and it then gave the appears of being contained.
I also am wondering if the difference in layout units between vh and % also plays into this.
I don’t think this is a bug, but more of a CSS foible.