Drop image on editor not quite working right

The feature where you can drag an image from Windows Explorer and drop it in the editor is pretty slick, except it seems not to be working quite properly.

Assuming Firefox, with the editor (Advanced) open:

You drag an image from Explorer into the editor area, and a gray mask (zwfreezediv) appears over the page.

If you now drop the image into the page, all goes as I think designed.

However, if you don't drop the image, but instead drag the image back out of the window, the grey mask stays, and there's no evident way to get rid of it.

That happens if you have the editor open, and you drag an image from Explorer to an image program, and happen to pass over the editor.

In addition, on inspecting the DOM when the mask is showing, it looks to me like zwfreezediv is supposed to display "Drop your files here". However that text is the same color as the mask, so it is invisible. This further obscures why the mask is there in the first place. And if the text color is going to be fixed, then it probably also should be much larger.

My issue tracking id: GWZ1024