Power Table and JComponent - strange border

I’m playing with “javax.swing.table.TableCellEditor” to make the table a little bit special.
I have a strange phenomenon when the component is a JCheckBox:
a small blue rectangle appears to the left of the cell.
has anyone else noticed this phenomenon?


	from javax.swing import AbstractCellEditor,JComboBox, JTextField, JCheckBox, SwingConstants
	from javax.swing.table import TableCellEditor
	from java.awt.event import ItemListener, ItemEvent
	import json		
	from shared.tools.pretty import p
	class myTableCellEditor(TableCellEditor, AbstractCellEditor):	
		def __init__(self, tableComponent):
			self.table = tableComponent
			self.editor = None
			# defind the options for the drop down
			self.options = []
		def getTableCellEditorComponent(self, table, value, isSelected, rowIndex, colIndex):
			#print 'sono qua'
			def str2bool(value):
				return value.lower() in ("yes", "true", "open", "on", "t", "1")
			self.options = json.loads(self.table.data.getValueAt(rowIndex,'options'))									

				if 'edit' in self.options:
					type = self.options['edit']
					print type
					if type in ['checkBox','comboBox']:
						if type == 'checkBox':
							print 'sono un check box'
							self.editor = JCheckBox()
						elif type == 'comboBox':
							print 'sono un combo box'
							if self.options['translation list']:
								lst_k = [k for k,v in self.options['translation list'].iteritems()]
								lst = [int(v) for k,v in self.options['translation list'].iteritems()]
								print lst_k
								print lst
								index = 0
									val = int(value)
									val = 0
								if val in lst:
									index = lst.index(val)
								self.editor = JComboBox(lst_k)
						print 'non so cosa sono'				
					# create a text field for default editor
					self.editor = JTextField(value)
					print 'sono un textfield'
				self.editor = JTextField()
				print 'disastro'
			return self.editor
		def getCellEditorValue(self):
			# is the editor a combobox?
			if type(self.editor) is JComboBox:
				# get the combobox value
				selectedValue = self.editor.getSelectedItem()
				# convert back to the options value
				newValue = self.options['translation list'][selectedValue]
			elif type(self.editor) is JCheckBox:
				return self.editor.isSelected()
				# get the text field value
				newValue = self.editor.getText()
			return newValue

	if colName == "value":
		m = myTableCellEditor(self)
		return {"editor":m}