We import InDesign pages into InDesign pages as graphics. Usually this works well, but sometimes not. Here's a case of "not." Basically, we import a page, crop it with the image frame to show just part of the page, and some of the cropped data shows up in the PDF despite being cropped out. I don't mean it's there, but hidden (which I expect because Crop Image Data to Frames doesn't apply to vector content) — I mean it's perfectly visible, as if we left it there.
Here's how it looks in InDesign (note that the content box ends below the art):
And here's what I get in an exported PDF (with annotation in red; it says "Folio of cropped page suddenly visible"):
This also happens without a containing text box (I can put just the imported item on a page by itself and replicate the issue). It also happens if the frame has a border on all four sides. But it only happens sometimes, and I can't find any meaningful difference between the cases where it happens and the cases where it doesn't. We can export the imported page as a PDF, then import the PDF instead of the InDesign file, but this wrecks our workflow. Any suggestions?