BUG #1853: explain gives ERROR: bogus varno: 23

The following bug has been logged online:

Bug reference: 1853
Logged by: Dustin Sallings
Email address: dustin(at)spy(dot)net
PostgreSQL version: 8.1b1
Operating system: Mac OS X 10.3.something
Description: explain gives ERROR: bogus varno: 23
Details:

If I run this query on my model:

select
sensor_id,
min(sample) as min_reading,
avg(sample) as avg_reading,
stddev(sample) as stddev_reading,
max(sample) as max_reading,
date(ts) as day
from
samples
where
ts >= (select max(day)+1 from rollups_day)
and ts < current_date
group by
sensor_id, day

It works by itself, but if I run it in explain, it fails with the following
error:

ERROR: bogus varno: 23

... I've so far been unable to make a standalone sample break because I
don't quite understand the problem.

samples is a view made of up union alls to a bunch of tables like this:

View definition:
((((( SELECT samples_1999.ts, samples_1999.sensor_id, samples_1999.sample
FROM samples_1999
UNION ALL
SELECT samples_2000.ts, samples_2000.sensor_id, samples_2000.sample
FROM samples_2000)
UNION ALL
SELECT samples_2001.ts, samples_2001.sensor_id, samples_2001.sample
FROM samples_2001)
UNION ALL
SELECT samples_2002.ts, samples_2002.sensor_id, samples_2002.sample
FROM samples_2002)
UNION ALL
SELECT samples_2003.ts, samples_2003.sensor_id, samples_2003.sample
FROM samples_2003)
UNION ALL
SELECT samples_2004.ts, samples_2004.sensor_id, samples_2004.sample
FROM samples_2004)
UNION ALL
SELECT samples_2005.ts, samples_2005.sensor_id, samples_2005.sample
FROM samples_2005;

I don't have any confidential data in this database, so I can provide the
entire thing if necessary, but it is a rather large database.