repaint in ToolWindow Follow

I have build an ToolWindow using

<![CDATA[myToolWindow = toolWindowManager.registerToolWindow(TOOL_WINDOW_ID, myPanel, ...)]]>

.
myPanel has an ActionToolbar on the BorderLayout.NORTH. An action from the toolbar add's a JLabel on the myPanel (at BorderLayout.CENTER) in it's actionPerformed() code .
When using the plugin, and lunching the action, nothing happens. Only when I hide and show again the tool window the modification are visible.
Can someone help me?
Thank You.