Chrome's Device Dimensions confuses Nimbus Capture

Chrome's Device Dimensions confuses Nimbus Capture

Chrome has an option to resize the browser viewport to some typical device size. When this option is used, Nimbus Capture generates a screenshot with the correct size, but with the actual screen contents too small.

For example, in the first screenshot below, the size I chose is 1024x768 and this is the size of the image that Nimbus Capture generated, but the actual contents only appear in about the top-left quadrant of the image.  You can check by right-clicking the image in this page, and opening the image separately.

I expect the contents to fill the image canvas, as per the second screenshot which I took with a different tool.