High Planning Time

I am running Postgresql on a Windows Server 2008 server. I have noticed
that queries have very high planning times now and then. Planning times go
down for the same query immediately after the query runs the first time,
but then go up again after if the query is not re-run for 5 minutes or so.

I am not able to find any specific information in the documentation that
would explain the issue or explains how to address it, so am asking for
advice here.

Here is an example.

explain analyze
select * from message
limit 1

"Limit (cost=0.00..0.44 rows=1 width=1517) (actual time=0.009..0.009
rows=1 loops=1)"
" -> Seq Scan on message (cost=0.00..28205.48 rows=64448 width=1517)
(actual time=0.007..0.007 rows=1 loops=1)"
"Planning time: 3667.361 ms"
"Execution time: 1.652 ms"

As you can see the query is simple and does not justify 3 seconds of
planning time. It would appear that there is an issue with my configuration
but I am not able to find anything that looks out of sorts in the query
planning configuration variables. Any advice about what I should be looking
for to fix this would be appreciated.