Mocha non-global references

Let's say I have a structure like so:

   /Users/me/Desktop...
    app/
     node_modules/
     subdir/
       test/
         mytest.coffee

If I cd /Users/me/Desktop/app/subdir, then run mocha tests like this:

/Users/me/Desktop/app/node_modules/mocha/bin/mocha --compilers coffee:coffee-script --require ../node_modules/coffee-script ./test --reporter spec --require should -t 5000 --colors -b

This works.

But when I change ../node_modules/coffee-script to /Users/me/Desktop/app/node_modules/coffee-script, I receive an error with a duplicate pathname:

Cannot find module /Users/me/Desktop/app/Users/me/Desktop/app/node_modules/coffee-script

Why is this? The use-case is that I'm trying to not pollute the global namespace from an NPM package, so it uses its install path + node_modules path for deps.