"Keep Proportions" Cuts Off Bottom of Page?

I’ve noticed that when I select “keep element proportions as the page is resized” on images and HTML elements, the bottom of my page is cut off in the browser. I couldn’t tell in debug mode because of the extra space at the bottom, but out of debug mode it cuts off the bottom when the page is loaded. Interestingly, as soon as I resize the window, the bottom of the page shows correctly.

Is this a known issue? Has anyone found a workaround? (I’m not using the new responsive engine yet–maybe that’s the only solution?)