If you search for an Entity from a drop-down field, such as contact on an activity...
After make you selection and click the lookup field again, for a split second any of the contacts for that entity are still available to select, but not long enough to select another one in the event you wanted to.
This is definitely a wish list item and not a bug, but I would find it useful for populating Cc or Bcc's on an email address.
