         var row:ConstraintRow;
         var hasContentSize:Boolean = false;
         var hasPercentSize:Boolean = false;
-        var rowHeights:Vector.<Number> = new Vector.<Number>();
-        
-        // Reset content size rows to 0.
+        var rowHeights:Vector.<Number> = new Vector.<Number>(numRows);
+        
+        // Start row heights at the minHeight of each row or
+        // its explicit height.
         for (i = 0; i < numRows; i++)
         {
             row = _constraintRows[i];

            }
            else if (!isNaN(row.explicitHeight))
            {
                var h:Number = row.height;
                
                if (!isNaN(row.minHeight))
                    h = Math.max(h, row.minHeight);

    
    /**
     *  @private
     */
    override mx_internal function get virtualLayoutSupported():Boolean
    {
        return false
    }
    
    /**
     *  @private
     *  Used to set new column widths before laying out the elements.
     *  Used by FormItemLayout to set column widths provided by the
     *  Form.
