[css-overflow] should overflowing zero-height or zero-width boxes be considered "overflow"?

I recently came across an interop issue related to how browsers treat zero-height or zero-width boxes in containers with overflow:scroll or overflow:auto.

In this test case:

http://codepen.io/psalas/pen/dYoevp

there are scrollers with various combinations of overflowing zero-height/width divs.  In Edge, all of the boxes have scrollbars (zero-height/width boxes count as overflow), but Chrome only has scrollbars in half of them, while Firefox has scrollbars in a few more cases than Chrome.

If we add a negative margin-bottom to the "tall zero-width" elements, Chrome and Firefox only show scrollbars in the four cases where the zero-width/height boxes contain non-empty (but not overflowing) content. 

What should the behavior be in these cases?

Thanks,
Peter