Mixins with meteor are acting strangely

I want to use _.mixin with lodash and underscore.string. In my lib/mixins.js, I put the following

_.mixin(lodash);          // lodash
_.mixin(s.exports());     // underscore.string

However, my meteor shell does not reflect this. When I check _.functions(_) or console.dir(_), the functions do not match lodash’s, it’s only underscore’s.

What’s the deal? How do I fix this?