If I create 2 identical shapes at same X-Y coordinates, giving the lower shape Black fill and higher shape White fill, I expect the white-filled shape to completely obscure the black-filled shape beneath it.

The actual behavior is that the lower black shape peeks out slightly from behind the white shape above it.

This seems to me like a SVG rendering issue because the visible black from the lower shape is irregular and doesn't get any bigger as you zoom in on it.

I've viewed this issue in Inkscape 0.92.5, Inkscape 1.2.1, and it also is reproducible in Chrome browser.

Does anyone understand what is going on here, and can it be prevented? If you're curious, my specific use case is creating silhouette white underlayer for UV printing purposes.

Attached here is an SVG that demonstrates the problem, also a screenshot of the SVG as rendered in Chrome.

I'm thinking it's probably a result of antialiasing.

Antialiasing can nominally be turned off in the document properties, but it doesn't work for me now. Probably a bug. I'm on 1.2, maybe it has been resolved in 1.2.1

I agree it's a rendering issue. Clearly the geometry is identical. 

The question is, then, how would this affect the end use...? As we see, the issue is independent of scale/resolution. I could be wrong, but maybe other vector design tools also have this issue.