watchman & fb-watchman - doc error, impl error, misunderstanding?

In fb-watchman’s README.md is the comment “change notifications are relative to the project root”. It appears this is for both watch and watch-project. However, when I run tests where I do a ‘watch-project’ on a dir 2 levels below the project root (what we seem to be calling the “watch root”), then change a file below that somewhere, the value returned is relative to the watch root, not the project root.

For example, I have ember project test123, in which the directory 'app' exists. If I do a 'watch-project' on 'app', then change the file app/styles/app.css, the change notification I get back is for file "styles/app.css", not "app/styles/app.css".

Is the documentation wrong, or is the implementation wrong? Or am I misunderstanding something?