I have this same problem and it's driving me insane. It started with a recent update as well.
The only way I've found to be able to add something to a blank page to keep it from jumping to the end is the use the Navigation Pane (View > check the box for Navigation Pane). So if I have a blank page, I select it in the pane then my cursor will actually show up on that page and I can type or paste stuff on that page. It works the same for pages with text/images already on it too. This isn't a fix though and I still end up on the last page by accident sometimes.
Another problem that started at the same time is Word randomly tries to close a file I have open while I'm working in another Word doc. I typically have 3-5 Word docs open at a time when I'm working, and it'll just chose a random one and ask to save before closing. I hit cancel and it's fine, but it's still annoying.