This was a long time ago, but the solution turned out to be pretty simple, just not obvious. In QV10 there was a Transparency feature added as a Document Property. The default was set at 100%, which meant that the usual Gray color for unavailable data turned white and the white unavailable data became invisible.
Solution: Settings -> Document Properties -> General tab. In the Selection Appearance section (bottom right), slide the Transparency slider back to roughly 20% and Apply. Everything shows back up. Adjust the Transparency setting until you find a level that works for you.
Note: In v11 the Transparenct slider has been limited to a maximum of 70%, so it is no longer possible to make the unavailable data disappear. I suppose you could tweak the text color to match and it might disappear, but why would you?
Hope this helps someone,