Updating cases in form creates blanks


In my project we have 2 groups of farmers: treatment and control. I used
Excel importer to bulk upload case data such as location and basic
demographics. This worked fine because all cases were visible in the case
list menu before continuing to open a form on the tablet.

Normally I would set all imported case properties as hidden questions in
the form and set the default response as the saved case property (as per CC

This time I have a few imported case properties that need to be updated in
the form (e.g. location), but ONLY for control farmers and not treatment
farmers. The questions for these case properties are not hidden in the form
so that mobile workers can update as needed. I also added a display
condition so that the location question is only shown for control farmers.
But the default response was still set as the saved case property.

The problem is that when I check the saved forms (without syncing) the
updated location for control farmers is saved to the case, but the location
data for treatment farmers is now blank.

What can I do to fix this? (aside from setting up a registration form)