If you were to checkout a packager project (say, MooTools Core) and put it in a directory that happens to equal the package name ('Core') then this expression would fail:
packager build Core/*
Because it would interpret this as an instruction to get files in that directory instead of from the package. Even if you do this:
packager build +components Core/*
You'll get the same error, something like this:
WARNING: The required component Core/Source could not be found.
WARNING: The required component Core/Tests could not be found.
WARNING: The required component Core/package.yml could not be found.