What are you using this ID for? ItemID isn't an html attribute, is it?
This method is for providing a non-unique string id that can be used by containers like TabPanel or Container to locate children. This value defaults to the actual id of the root element, but doesn't have to be set to that.
* Sets the widget's item id. Unlike a widget's id, the widget's item id is
* not tied to id attribute of the widget's root element. As such, the item id
* does not have to be unique.
* @param id the item id
Try setId(String) instead?