Natron 2.4.1 win10

when I run:
myknob = currentNode.getParam('enablePreview')
myknob.setValue(True)
print 'testtrue'
currentNode.refreshUserParamsGUI()

Expected:
preview should appear in graph. Actually only checbox change in the properties

Notes:

• the same script for "disableNode" works ( big cross over node is drawn in graph)
• the preview appear as soon as I MANUALLY change any knob value in the properties

Some refresh code that is run in the UI should be executed from the python backend ?