Public Class Form1
    Dim table As New DataTable
    Private Sub UltraButton1_Click(sender As Object, e As EventArgs) Handles UltraButton1.Click
        Me.UltraGrid1.Rows(0).Cells(0).Value = "Value after setting UltraGridCell.Value"
        MessageBox.Show("RowState = " & DirectCast(Me.UltraGrid1.Rows(0).ListObject, DataRowView).Row.RowState.ToString)
        table.AcceptChanges()

        Debug.WriteLine(table.Rows(0).RowState)
    End Sub

    Private Sub UltraButton2_Click(sender As Object, e As EventArgs) Handles UltraButton2.Click
        DirectCast(Me.UltraGrid1.Rows(0).ListObject, DataRowView).Row.Item(0) = "Value after setting DataRow.Item(0)"
        MessageBox.Show("RowState = " & DirectCast(Me.UltraGrid1.Rows(0).ListObject, DataRowView).Row.RowState.ToString)
        table.AcceptChanges()

        Debug.WriteLine(table.Rows(0).RowState)
    End Sub

    Private Sub UltraButton3_Click(sender As Object, e As EventArgs) Handles UltraButton3.Click
        Me.Reset()

    End Sub

    Private Sub Reset()

        table.Columns.Add("Column1", GetType(String))
        table.Rows.Add("Initial value")
        table.AcceptChanges()
        Me.UltraGrid1.DataSource = table
    End Sub

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Me.Reset()

    End Sub
End Class

Please make the table global and then you can call 

table.AcceptChanges()

Then when you click the second button it will display the rowstate as modified. 

Thanks very much for the quick response, and you're absolutely right.  I assumed that this was new behavior simply because we ran into it after the upgrades, but now that I created a .NET Framework 4.7.2 / Infragistics 18.2 project I see that it's the same behavior.

I do find it odd that the DataRow is somehow updated while still reflecting a RowState of Unchanged, but since this is not new behavior as I originally assumed it's probably not worth trying to change.  We'll just try to remember that when RowState matters, we can't set the cell value directly but instead must set the value in the DataRow.

I apologize for the confusion.  Thanks again for all your help Michael!