The BasicDialog, which is great by the way, seems to popup centered on the browser by default, making the rest of the page go gray.
However, when the dialog is tied to an element far down on the page, even scrolled way down, the BasicDialog pops up at the center of the top of the page (off and above the screen), and the portion marked gray is far above the button the user clicked.
For an example, use the Hello World application, and create a second button far, far, below the first one, so that you have to scroll down to get to it. You'll see, when you click that button, the dialog is created up above (at the top of the page), not where the page is scrolled to currently.
What to do?