I've run into the same issue, and it appears to depend on the length of the first paragraph (the one with the drop cap) and the size of the window.
If the first paragraph is short, then the bottom of the drop cap falls within the next paragraph, and the reader appears to think it belongs with that one, instead of the first one. If your window size is small, then it moves the drop cap it to the next page, along with the next paragraph.
I happen to have that book (Nighthawk), and can get the same behavior to happen by shrinking the size of my reader window.
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