What spec? I just looked up what the issue is with vh on mobile and the very first resource I found talked about how the spec isn't clear on how it's supposed to behave in the presence of movable chrome, like the address bar on mobile browsers.

It also says that Safari's initial implementation updated `vh` when the address bar changed visibility and this caused a bad jump in layout, which is why they changed it to ignore the address bar so it's a fixed value instead. And it says Chrome mobile followed suite as well, which means it's not just Safari that thinks the "fixed value" approach is better on mobile.