There is some weird issue with Internet Explorer WebDriver that I’ve encountered in IE8 (not sure about newer IE versions) – the image with URL “about:blank” causes WebDriver to be stuck forever in “1 item remaining (downloading picture about:blank)”.
Looks like it has never been resolved.
It also turned out that in my case “about:blank” images were coming from Progressive IE which seems to be using it for background images for some reason (see screenshot of part of PIE2 code for an example of such image).
Disabling PIE in test mode solved the issue. Though other people had it in different cases with different workarounds.