Version and Project custom fields show incorrectly in change history and email notifications

Custom fields that are not simply text (eg. Version and Project Picker types) do not display correctly in the change history when edited. The database ID shows, instead of a human-readable value. Eg. the change history when changing a Version custom field value:

Scheduled Fix Version 10000 10002

and in an email notification:

Test User updated TP-20:
------------------------

Scheduled Fix Version: 10002 (was: 10000)
ProjectPicker: 10000