Web ADI templates
As per my understanding, When a template is not Read Only but the GLDI: Journal Source profile option is set to "Spreadsheet", within Oracle versions 12.1 - 12.2.x, the profile option "GLDI: Journal Source" having a value of "Spreadsheet" at the site level will render the source field read-only regardless of the read-only field setting at the integrator and layout level.
As such, even though WEB ADI templates do not have the journal source field set to be read only, the system enforces the source field of these templates to be "Spreadsheet" and does not allow the user to update this source.