_.template render result is a function not a String in node js

I'm using underscore js as a module in my express 4 application. I use the template function but the result returns a function object instead of a rendered String. I Finnally solved this by updating my package.json to "underscore": "~1.6.0" instead of "underscore": "^1.6.0". Is there any major change on how to use template function in underscorejs version 1.6.0 above or it's just a bug ? thanks in advance