To reproduce: add a RadGridView and a RadButton on the form. Use the following code snippet:

public RadForm1()
{
    InitializeComponent();
    this.radGridView1.Columns.Add("Col1");
    this.radGridView1.Columns.Add("Col2");
    for (int i = 0; i < 5; i++)
    {
        this.radGridView1.Rows.Add(i, "Item" + i);
    }
    this.radGridView1.AutoSizeColumnsMode = Telerik.WinControls.UI.GridViewAutoSizeColumnsMode.Fill;
    this.radGridView1.RowValidating += radGridView1_RowValidating;
    this.radGridView1.UserAddingRow += radGridView1_UserAddingRow;
}

private void radGridView1_UserAddingRow(object sender, Telerik.WinControls.UI.GridViewRowCancelEventArgs e)
{
    e.Cancel = true;
}

private void radGridView1_RowValidating(object sender, Telerik.WinControls.UI.RowValidatingEventArgs e)
{
    if (e.Row.IsModified && e.Row is GridViewDataRowInfo)
    { 
        e.Cancel = true;
    }
}

private void radButton1_Click(object sender, EventArgs e)
{ 
    RadMessageBox.Show("Clicked");
}

1. Select a data cell and activate the editor. Enter some new value and click the button. The Click event is fired.
2. Select the new row and activate the editor. Enter some value and click the button. The Click event is NOT fired.

Workaround: use the CellValidating event instead.