Sharepoint 2010 OOTB Approval Workflow >> Open this Task button calls infopath form

Question

I'm customizing the Sharepoint 2010 OOTB Approval workflow's "Överall" behavior step.

In Step #3, I want the user to directly open the Approve/Reject infopath form in a modal window... (like its doing from the Outlook >> Open this task button ribbon)

As suggested in this post:

http://social.technet.microsoft.com/Forums/en/sharepoint2010customization/thread/7e85ef43-bde3-43e0-abbe-298ff87a5f49

If I refer Form_URN & IsDlg=1,

1. it doesn't open a modal window and
2. if the user clicks "Approve", the process is completed but the page still shows the following message.

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