underscore interpolate settings

I'm trying to use handlebars style templating with underscore in backbone (with require.js). I have the following:

_.templateSettings.interpolate = /\{\{(.+?)\}\}/g;

In my templates I have set up a test:

<div><%= title %> | {{ title }}</div>

I get the following in the browser:

Correct title | {{ title }}

So it looks like the standard underscore template settings are working and the handlebars style ones are getting ignored:

But if I check in the console in chrome I get this (which looks to me like it should be correct)

_.templateSettings
Object {evaluate: /<%([\s\S]+?)%>/g, interpolate: /\{\{(.+?)\}\}/g, escape: /<%-([\s\S]+?)%>/g}

Any ideas why this isn't working correctly?