InDesign won't add new pages to end of doc

I’m building a doc page by page. When I need to add another page, I find that InDesign will randomly add it to the end of the document or insert it in between the last and next-to-last pages… even though no page is selected in the Pages panel.

When InDesign decides to insert rather than append a page, I can almost always Undo and then repeat the operation… and it’ll be appended as expected.

But right now, InDesign refuses to append a page to the end of the document.

I think we’re all just so used to these defects that the shoddiness has become normalized. But it shouldn’t be, ever.