When creating blueprints in the sandbox with all of pY's mods enabled, tiles "asphalt" and "coal tile" are added automatically. If there is no water, landfill or related tiles, I would assume that no tiles would be added.

Workaround: Remove all tiles in the blueprint.

This is simply how Factorio works when using the data that the Py mods have purposefully set altered from the base game. pyindustry converts the standard lab-dark-1 and lab-dark-2 tiles into its own coal and asphalt tiles.

Why do they do that? I don't really know. But, they're the ones who did it, and there's not much I can do about it. It affects anything lab-like that utilizes that data.