Extending DataGrid using same class name

programming flash
1

I have class that subclasses fl.controls.DataGrid. The function below from the DataGrid superclass throws a compile time error (implicit conversion fl.controls.DataGrid to DataGrid) when the subclass resides in an unnamed package.

If I place the subclass in a named package, the error disappears. If I use a different class name (e.g. DataGrid2), the error disappears.

I never intended to leave the subclass in an unnamed package. However, I am curious as to why the unnamed package is preventing the compiler from seeing that DataGrid is a subclass of fl.controls.DataGrid. Any ideas?

  public function addColumnAt(column:*, index:uint):DataGridColumn {
   var dataGridColumn:DataGridColumn;
   if (index < _columns.length) {
    // insert placeholder for new column
    _columns.splice(index, 0, "");
    // adjust colNums
    for(var i:uint = index + 1; i < _columns.length; i++) {
     dataGridColumn = _columns* as DataGridColumn;
     dataGridColumn.colNum = i;
    }
   }
   var col:* = column;
   if(!(col is DataGridColumn)) {
    if (col is String) {
     col = new DataGridColumn(col);
    } else {
     col = new DataGridColumn();
    }
   }
   dataGridColumn = col as DataGridColumn;
   [COLOR=red]dataGridColumn.owner = this;[/COLOR]
   dataGridColumn.colNum = index;
   _columns[index] = dataGridColumn;
   invalidate(InvalidationType.SIZE);
   columnsInvalid = true;
   return dataGridColumn;
  }