Datagridview disabling a column in FormLoad does not work?

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VB

I encountered a strange behavior with the following code on a datagridview in VB2010. dgv is the name of the datagridview. In FormLoad, I wrote

Private Sub frmdataLog_Load(sender As Object, e As System.EventArgs) Handles Me.Load
    dgv.ColumnCount = 5
    dgv.Columns(0).Width = 27
    Dim j As Integer
    For j = 1 To 4
        dgv.Columns(j).Width = 85
    Next

    dgv.Rows.Add(1)
    dgv.Columns(0).HeaderText = "Sl No."
    dgv.Columns(1).HeaderText = "Test Reading Nm"
    dgv.Columns(2).HeaderText = "Standard Reading Nm"
    dgv.Columns(3).HeaderText = "Error in Nm"
    dgv.Columns(4).HeaderText = "% Uncertainty"
    For j = 0 To 5
        dgv.Columns(j).ReadOnly = True
        dgv.Columns(j).SortMode = DataGridViewColumnSortMode.NotSortable
    Next
    dgv.Columns(1).ReadOnly = False

End Sub

I am expecting column(1) to be editable while all other columns will be uneditable.

But I found that even column(1) is also readonly!

But when I added the following code, the problem got solved:

Private Sub dgv_CellEnter(sender As Object, e As System.Windows.Forms.DataGridViewCellEventArgs) Handles dgv.CellEnter
    colVal = e.ColumnIndex
    rowVal = e.RowIndex
    If dgv.Columns(1).ReadOnly = True Then
        dgv.Columns(1).ReadOnly = False
    End If
End Sub

My question is why does the line dgv.Columns(1).ReadOnly = False not execute under Form load?