Ah you downloaded the 'relic'd version. There's also a version available with most of the screen-printing missing above the knobs and some gouges out the woodwork**I joke of course, I'm sure someone will be along shortly who can help you. What happens if you try to click on that missing key with your mouse, does it not force a redraw?
That's strange. i'm really not sure what's causing it. Thankfully it's just a graphical issue and I assume it works fine from your DAW or midi keyboard.