I frequently get a black vertical bar as the resulting image, and occasionally a vertical bar filled with junk (such as a bunch of Google +1 buttons) when I take a screenshot using Alt-PrtScn. Control-PrtScn does not have the problem, but of course, these are different screen shots.
This is on Windows 7 using the latest stable release, 1.1.5 Build 2642 (64 bit). Attached you can see a sample screen shot that I took from an IE 10 window (needless to say, this is not what the web page looked like, nor is it even remotely the size of the window that was being used). The bar seems to always be approximately the same size (70 pixels wide x 376 pixels tall) regardless of window size.