Basically, when either the content or the sidebar (or both) have a full width image, they won't resize fluidly when the browser window is being resized. Here's a page without any image in the content or sidebar:
Chrome (and I presume other WebKit/Blink browsers as well) doesn't have this problem. Does this have anything to do with "display:table-cell" that you suggested here? I tried Asteroid and it seems to have the same problem.
The screenshots are from my local WP installation, but my blog is running the same code.