Hook_filter, no cache?

mysql> SELECT cache FROM filter_formats;
+-------+
| cache |
+-------+
| 0 |
| 0 |
| 0 |
| 0 |
+-------+
4 rows in set (0.00 sec)

Message.module which returns TRUE for hook_filter() with an $op of 'no cache'. A comment in the code suggests that this may be for development only, it says:
"No caching at all, at least for development"

Why is this in here? We are manually enabling for some of our caches with:

UPDATE filter_formats SET cache = 1 WHERE format IN (1, 2, 5);

This issue first spotted in http://www.mothersclick.com where memcache bin where cache_filter was empty with 38,759,794 cache misses. Oops.

Issue tracked down by Jeremy @ http://tag1consulting.com/