When browsing files which are present in the filesystem but not added in the repository are shown.

$ fossil new test.fossil
$ fossil open test.fossil
$ fossil server&

now should show an error as should

$ echo Hello World! > index.wiki

now should show "Hello World!"

$ fossil commit

Now since the file was not added it is not committed and hence still shows an error.
should have been showing something like "file not added to repository" all the time so that it is consistent with the committed state created by committing the checkout.