When creating a page in the Page: namespace, moving between editors can move the header and footer into the body.
- Go to https://en.wikisource.org/wiki/Index:Sandbox3.djvu
- Click on any Page: redlink, ensuring that you land in the source editor
- Switch to Visual Editor
- Switch back to source editor
- The header and footer are now in the body between <noinclude> tags.
- Save the page in source mode.
- Observe that the page status bar is now duplicated. Edit the source again to see that the <noinclude>d header/footer have remained in the body.
I came across this while working on https://en.wikisource.org/wiki/Index:Life,_Death,_and_Immortality.pdf so this isn't to do with the funky setup of Index:Sandbox3.djvu.