Using createPage() twice for the same phantom instance

I'm trying to set up mocha tests with PhantomJS and I've encountered a problem where I can't use the same phantom instance to create multiple pages. The first test case runs just fine, but the second one times-out. I'd like to use just one instance, because it should be faster.

var assert = require('assert');
var phantom = require('phantom');
var path = require('path');

var ph;

describe('document', function() {
    before(function(done) { // Create only one phantom instance for the whole suite
        this.timeout(10000); // Prevent test case from aborting while phantom loads
        phantom.create(function(p) {
            ph = p;
            done();
        }, {
            dnodeOpts: {weak: false}
        });
    });

    it('should have a title', function(done) {
        ph.createPage(function(page) {
            var url = 'file:///' + path.resolve(__dirname + '/index.html');
            page.open(url, function(status) {
                page.evaluate(function() {
                    return document.title;
                }, function(title) {
                    assert.equal('This is a title', title);
                    ph.exit();
                    done();
                });
            });
        });
    });

    it('should have the same title', function(done) {
        ph.createPage(function(page) {
            var url = 'file:///' + path.resolve(__dirname + '/index.html');
            page.open(url, function(status) {
                page.evaluate(function() {
                    return document.title;
                }, function(title) {
                    assert.equal('This is a title', title);
                    ph.exit();
                    done();
                });
            });
        });
    });
});

Why won't it open the page the second time?