mandatory user reference

Hi,

I have built a site using drupal and cck (www.plusgroups.org.uk) and it's working well, we're using cck user reference and it is a mandatory field for booking officers of events. If the submitter enters a space (just a space character) and doesn't select a user from the list the mandatory condition of the field is satisfied (!) and so the item is submitted.

This bug doesn't seem to affect node reference fields.

Richard