BUG #3925: You can delete enum elements from pg_enum, but it is used in a table

The following bug has been logged online:

Bug reference: 3925
Logged by: Stefan Kunick
Email address: stefan(at)kunick(dot)org
PostgreSQL version: 8.3RC2
Operating system: Windows Longhorn
Description: You can delete enum elements from pg_enum, but it is
used in a table
Details:

I create a enumeration. After this, i used the enumeration in a table. I
delete the enumeration in the table pg_enum (delete from pg_enum where
enumtypid=16631 and enumlabel='center'; The delete don't check, that the
element is used in a table.

When you access to the table some programs stopped with a error.

Can we check in the delete statement that the element ist used in a table?