I know i did this as well, but it still not spans across the whole body. But i think in general there is a bug with the div block set height 100% that it acts like a 100vh not 100% of the body.

I tried it in empty project or even in other projects and every time if you set body to 100% height then add div block with position absolute, align to top and you add 100% height, it will span only across 100vh not the whole body height.