Any UR item can have notes added via the Item Notes pane:
http://www.kinook.com/UR/Manual/itemnotespane.htm
Are you saying that the Item Notes pane selectively disappears and can't be accessed (via View | Other Windows | Item Notes or Ctrl+5) for some items? Please post the info from Help | About | Install Info, a detailed description of the problem and steps to reproduce, and possibly a screenshot if relevant. Thanks.