Hi,

Thank you for the update and I’m glad the question was resolved.

Please let me know if I can be of further assistance.

Turns out that I was setting ExpansionIndicatorVisibility to Hidden instead of Collapsed in the InitializeRecord and RecordExpanded event handlers as illustrated below: 

        private void DataGrid_InitializeRecord(object sender, InitializeRecordEventArgs e)

        {

            if (e.Record.HasChildren)

                e.Record.ExpansionIndicatorVisibility = Visibility.Visible;

            else

                e.Record.ExpansionIndicatorVisibility = Visibility.Hidden;

        }

        private void DataGrid_RecordExpanded(object sender, RecordExpandedEventArgs e)

        {

            var childRecord = e.Record;

            if (childRecord.ViewableChildRecords.Count > 0)

                childRecord.ViewableChildRecords[0].ExpansionIndicatorVisibility = Visibility.Hidden;        }

Changing ExpansionIndicatorVisibility  for the record from Hidden to Collapsed fixed this.

I have styles defined for the  CellValuePresenter but none of  them explicitly alter the ExpansionIndicator.  It is a tricky one.