What seems to be happening is that when you click on the label sprite, you move the info sprite below the mouse pointer and then the very next event thinks you've clicked on the info sprite and hides it again.
You could seperate the clicking and the showing/hiding logic like this:
<img src="http://dl.dropbox.com/u/8367729/construct/pics/showHide.png" border="0" />
Another thing to be aware of is that when you show the info box, the buttons are still below it and can still be clicked. So you'd want to move them offscreen or disable them in some way.