Hello Telerik Support Team,

We are encountering an issue in **Telerik PivotGrid for Blazor (v12)** related to field selection behavior.

**Issue Summary**
When a field is selected from the field list/configurator, it is correctly added to the **Columns** area. However, when the same field is later unchecked (removed), it continues to remain in the Columns section and is still displayed in the report.

**Steps to Reproduce**

1. Load the PivotGrid with data.
2. Open the field list/configurator.
3. Check a field (e.g. InternetOrderID) to add it to the report (it appears in the Columns area as expected).
4. Uncheck the same field to remove it.
5. Observe that the field still appears in the **Columns** section and remains visible in the grid.

**Actual Behavior**
Unchecking a field does not remove it from the Columns area. The field remains active and visible in the PivotGrid.

**Expected Behavior**
When a field is unchecked in the configurator, it should be fully removed from the Columns area and no longer displayed in the grid.

I have added a zip file for reference.

Regards,
Niraj Phalke