InfoPath version setting and its effect on existing forms

I was working with an existing form library. Template for this form library is published with some fields and users wants to capture more information on the form. So we decide to add couple of more fields on the forms. In past I have no problem adding new fields or groups to the form unless I am promoting the fields as site columns (after certain limit your forms times out before it can publish). I made few changes and published the form, everything worked on new form. Users where able to go and save all the information on the form and submit it to form library. Issue occurred on existing forms, all the forms which were created before publishing the template showed new fields as read only or display only. I never had this issue so I was bit surprised with this behavior. After looking around on web I came to two possible source of errors:

1) For some reason version number of the form is not updated. This is can easily fixed by going to Tools –> Form Options –> Versioning  and updating the version number manually.

2) You have not chosen “Automatically upgrade existing forms” option in “On version upgrade” drop down on the versioning tab. Other options is to “do nothing” or “use custom events” which allows you to bind a custom event handler that you can code in visual studio.