Cannot update promoted fields from Library for InfoPath form update

I have recently been testing an upgrade to an existing site and came across a phenomenon that had me completely stumped.  To give you an idea of what I was dealing with, the existing system has:

• An InfoPath form
• 2 Promoted fields linked to existing columns in the Forms Library
• A Nintex workflow to change the value of the above promoted fields in the Forms Library

We made a change to the form and gave it a new version – Version 2.  The Updated system would now have:

• 2 InfoPath content types installed (Version 1 and Version 2)
• Version 2 promotes two different fields to the same columns in the Forms Library as Version 1 mentioned above. 
• The same Nintex workflow runs against Version 1 and Version 2 of the form. 

Having 2 InfoPath forms installed meant that I had to make sure that I still had data integrity whether using Version 1 or Version 2 of the InfoPath form.  This is where the problem came in...

PROBLEM:

As I mentioned earlier,  the Nintex workflow would be updating the Form Library columns where the InfoPath fields were promoted to.  But as I ran through the system I realised that, while the workflow was still updating the promoted fields for the Version 1 form, it wasn't doing the same for Version 2 forms.

I tried everything from logging extra notes in the workflow history to make sure the workflow actually tries to update Version 2 to changing the fields that the workflow was updating, you name it!  Well, it finally came to me.  One connection lead to another connection and BOOM – LIGHT BULB! 

SOLUTION:

When you publish an InfoPath form and you have a promoted field, by default a user cannot edit that field directly in the Form Library.  It is a read-only column.  But, if you modify the Column you want to promote, you will see a tick box option available to you:

"Allow users to edit data in this field by using a datasheet or properties page"

When you select this option, you make the field value editable in the Form Library.  For a detailed explanation of how to set this option, see David Gerhardt's blog: Promoting Editable SharePoint Columns.

My problem was that, where the InfoPath form Version 1 promoted fields had this option ticked when it was published, the new fields being promoted in Version 2 did not, and that caused the conflict.