Chrome: jbpm-forms-rest-integration.js errors when working with task forms

Description of problem:
When using google chrome (current latest version 39) When I load a process startform / task form using jbpm-forms-rest-integration.js app and then try to use the form (i.e. start process, claim / complete task) I'm getting javascript error: undefined is not a function.

The error seems to be caused by line 9 in jbpm-forms-rest-integration.js:
lastConfig.host.startsWith(event.origin)

-> lastConfig is not null, but host is null;

Version-Release number of selected component (if applicable):
BPM Suite 6.1.0 ER6

How reproducible:
Always

Steps to Reproduce:
1. Open process start form loaded using jbpm-forms-rest-integration.js in google chrome
2. Start the process using this form

Actual results:
Javascript error in browser javascript console (F12) and the function defined by "successCallback" / "errorCallback" parameters in showStartProcessForm are not called

Expected results:
No javascript error, and success/error callbacks are called.

Additional info:
Attached simple web app used for testing embedded forms feature