Why Is My Shared Family Content Grayed out for One Member

For some time now, our son has been unable to download most--but not all--the video content (TV/Movies) I purchase under Family Sharing. Other members of our household (4 total) have no problems accessing the same content. Also, his problem does not appear to extend to music.

The symptoms are these: if he goes to Family Purchases, and clicks on my name, my purchases appear there, but only a few of them are downloadable. These have the familiar cloud/downarrow icon on them. In list view, the others are grayed out. Clicking on the grated out shows does nothing.

There is no rhyme or reason to which shows will be unavailable. For instance, I purchased a Stanley Kubrick movie bundle from iTunes, a single purchase; about half the movies are accessible to him, the others aren't. I purchased a Season Pass to the BBC Sherlock; the first episode is unavailable, the rest are. And so on. The last straw was an episode of The Sopranos I just purchased for us to watch at each end of the country. He can't access it.

Just to confuse the issue further, HIS relatively few purchases are MORE accessible by me than by him. His own Boardwalk Empire episodes are all grayed out under his login on iTunes, for example, but I can download them from his Purchases in my account. Again, music seems unaffected.

Now, since he can see all my purchases, I assume we don't have to question whether Family Sharing is set up correctly, but in case anyone wonders, I've gone through Apple Support's entire checklist. Nothing looks unusual. On his account page it says that he is part of my family, and I am the organizer of the account.

Any ideas much appreciated.