After doing some radical changes in xdocs I noticed that there was still an old index.html in build/site that was not updated because it was no longer part of the site. It should definitely have been removed.
It doesn't by default for performance reasons. During development it is usually not important if the odd file is left hanging and cleaning a directory with a few thousand files in it can take quite some time.
If you want to do a clean build then do 'forrest clean site'
Ross
