Also, my assumption about what would happen if I used the tag command was wrong.
If instead of putting tags in my changelog XML, I comment out changes 3 and 4, run through with changes 1 and 2, use the tag command with version 1.0.0, then uncomment changes 3 and 4, run through the changes again, and then use the tag command with version 1.1.0, things behave as I would expect.