At the moment, Google is playing tricks with me again and not returning PRs for most of top 14 listings - including yours. To study what's happening with the pages above you, and comparing them to yours, would take quite a bit of time but, from what you've said, it shouldn't be happening.
However, it is happening and you need to take action. Do all or most of the page's IBLs include the word, "apocrypha"? Have you checked?
I can tell you that, even before Google was launched, Brin and Page talked about including the text around the links in the ranking algo, and they've probably done something about it since then so, to some extent, links may well be themed as you suggested.
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I should have said that, when I'm placing a link on an off-topic page, just for the sake of the link, I usually write a little bit of on-topic text around it - especially in front of it. It's just in case Google has implemented B&P's thoughts.
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