BUG #6426: Complex query runs 10 times longer with "LIMIT 20"

The following bug has been logged on the website:

Bug reference:      6426
Logged by:          Andrew Schetinin
Email address:      aschetinin@gmail.com
PostgreSQL version: 9.1.2
Operating system:   Debian Linux
Description:=20=20=20=20=20=20=20=20

I have a complex query that, when unlimited, runs in 2.5 seconds and returns
400+ records.

The same query, with added "LIMIT 20 OFFSET 0" at the end, runs 25 seconds!
(and returns correct 20 records)

I think there is a bug in the query optimizer. Other variations of this
query (with slightly different constraints and joins) work fast with and
without LIMIT.=20

The same query works fast in PostgreSQL 8.4 (tested on another machine with
Ubuntu and not exactly the same but very-very similar database).

I can provide the query execution plans of the two cases (as long as they
are not published on the Web); but not the database because there is
customer's data in it.

Please let me know if anybody is interested in researching the problem.

Regards,

Andrew Schetinin