Unable to pre-populate fields that are not on the main level of a form structure

Problem/Motivation

Unable to pre-populate fields that are not on the main level of a form structure.

Steps to reproduce

Create a CSV file with proper keys and data but put the field in a fieldset on the form

When you try to import the data, you get :
The Webform element keys are not matching at least one CSV column.
There was and error while saving the prepopulate file into the database.

Proposed resolution

Make it so field at any levels in the form can be pre-populated