I am not maintaining button state in my plugin

Newbie question:

I have made some custom buttons in a plugin. I enable/disable them depending on whether the user selects a radio button or not.

The problem is, whenever I click in the editor all the buttons become enabled again. I don't know how to detect the state and keep it if I'm not creating the buttons.

Any help would be appreciated.

Code for plugin buttons:

var AddMyButton=function() {this.name = 'MyButton';}
AddMyButton.prototype.Execute=function()   
{
  var oEditor = FCKeditorAPI.GetInstance('fcksequence') ;
  oEditor.InsertHtml('<b>Wow bold text!  Who would have thought this is possible?</b>');
}
AddMyButton.prototype.GetState=function() 
{
   return FCK_TRISTATE_ON;  
}
var oMyButton=new FCKToolbarButton('MyButton', 'MyButton', 'MyButton does cool stuff', FCK_TOOLBARITEM_ONLYTEXT,false,true);
FCKToolbarItems.RegisterItem('MyButton', oMyButton);
FCKCommands.RegisterCommand('MyButton',   new AddMyButton());

Javascript code for radio button

  var oEditor = FCKeditorAPI.GetInstance('fcksequence') ;

  var idx = whichSequence();
  switch(idx)
  {
  case '1':
    oEditor.EditorWindow.parent.FCKToolbarItems.LoadedItems['MyButton'].Enable();
    break;    
  case '2':
    oEditor.EditorWindow.parent.FCKToolbarItems.LoadedItems['MyButton'].Disable();
    break;
  }

Any help is appreciated.

Thanks,

biff