Another possibly related issue cropped up before my posts were going through:
Once in a while the Tree gets glitchy, and I suspect it involves interaction with the tabs, or code in common. A few minutes ago, I couldn't scroll all the way down the tree, or all the way right in the tabs. The icons in the tree had fragments of text in them, different text in each one, only a letter and a half. The scrollbar didn't work right, and the whole tree and scrollbar flickered when I dragged down, trying to reach the last few chapters. It's moderately repeatable -- the scrollbar must be all the way down.