I am not too sure if this will solve your problem, but I have two ideas:
Firstly, you are sure that the text isnīt part of the image? silly question but must be asked.
Secondly, try moving your setText("") down a few lines, just before toolBar.add() method. or try use a different constructor: ImageIcon copyIcon = createImageIcon ("images/copy.gif");
I am not sure if this will solve your problem but I canīt see where else the problem is coming from.
Does the text still show if there is no image on the button?
I think, therefore I am....... I think.