Create a new user filling out all fields in the Elliott's Guest Profile form.
Log in as that user.
Register for this event: http://sandbox.devel.civicrm.org/civicrm/event/info?reset=1&id=35
Only those non-custom fields are pre-filled. The others (custom in that profile) are blank.
This seems to be a permissions problem. On my system I cannot even get it to pre-fill any entries.