profile with no label for custom data field causes error in email template

Discussion here:
http://forum.civicrm.org/index.php/topic,14883.0.html

To reproduce:

• create a custom data field with multiple checkboxes attached to participant records
• create a profile that includes this field, but has no label
• add the profile to an event registration page
• use ONLINE registration page

confirmation email displays the data as "0th, 0 12:00 AM"

For OFFLINE registration, in which the custom data is entered directly into the custom data group and not via a profile, the confirmation emails still just say "Array". Problem seems to be that template doesn't handle $optionsPerLine properly.