Check for any custom mappings that may be set incorrectly to include import instead of just export if using out of the box Clarity fields.
Example: If mapping prStart and prFinish in Clarity to anything custom, check to make sure these are set to just export. If they include import, those dates can instead get incorrectly saved back to Clarity.
Steps to check/correct:
1. In Clarity go to Administration->Project Management->MSP Field Mappings
2. Click on the link for any custom field mapping that is incorrectly set to import and export instead of export.
IMPORTANT: Leave any out of the box mappings as defaults set for import and export
3. Change Data Operation to just Export and Save changes