Help with problem using wildcard in string value expression

(I first asked for help under postgres-sql, but this looks like it
isn't an sql problem after all.)

I've got a strange problem with wildcards (postgresql 7.0.2).

On some tables, the character combination '.%' in a pattern
prevents the pattern from every matching.  But on other tables
the combination works fine.  The attached script output shows
the problem.  I see this in several different databases, but
so far only in databases with more than a few rows, and with
indices.  This is a typical example (I've annotated the output
with a couple of comments, look for lines starting with "> ".

If anyone can explain (a) why I'm seeing this behavior and
(b) what I can do to fix it, I'd be eternally grateful.

Thanks!
--
Steve Wampler-  SOLIS Project, National Solar Observatory
swampler@noao.edu> *********************************************************************
> *********** Note: "messages" has 35129 rows.  '.%' doesn't work *****
> *********************************************************************

logdb=# \d messages
           Table "messages"
 Attribute  |     Type     | Modifier
------------+--------------+----------
 time_stamp | varchar(32)  | not null
 category   | varchar(32)  |
 client     | varchar(128) |
 message    | text         |
Indices: category_id,
         client_id,
         time_stamp_id

logdb=# select count(*) from messages where client like 'kp.dhs.v%';
 count
-------
  2955
(1 row)

logdb=# select count(*) from messages where client like 'kp.dhs.%';
 count
-------
     0
(1 row)

logdb=# select count(*) from messages where client like 'kp.dhs%';
 count
-------
  2955
(1 row)



> *********************************************************************
> *********** Note: "messages.2000_195-2000_220" has 28496 rows
> ***********       and was created via a "SELECT * INTO TABLE ...."
> ***********       from "messages".  Note that '.%' works here!
> *********************************************************************

logdb=# \d messages.2000_195-2000_220
  Table "messages.2000_195-2000_220"
 Attribute  |     Type     | Modifier
------------+--------------+----------
 time_stamp | varchar(32)  |
 category   | varchar(32)  |
 client     | varchar(128) |
 message    | text         |

logdb=# select count(*) from "messages.2000_195-2000_220" where client like 'kp. dhs%';
 count
-------
 17657
(1 row)

logdb=# select count(*) from "messages.2000_195-2000_220" where client like 'kp. dhs.%';
 count
-------
 17657
(1 row)

logdb=# select count(*) from "messages.2000_195-2000_220" where client like 'kp. dhs.v%';
 count
-------
 17657
(1 row)

logdb=# \q