BUG #6512: Bug with prepared statement and timestamp + interval

The following bug has been logged on the website:

Bug reference: 6512
Logged by: Stefano Baccianella
Email address: stefano(dot)baccianella(at)gmail(dot)com
PostgreSQL version: 9.1.1
Operating system: Windows 7 64bit
Description:

When trying to execute a query like:

SELECT * FROM table WHERE
timestamp_column > $1
AND timestamp_column < $1 + interval '1 hour'

There is no problems, but when executing

SELECT * FROM table WHERE
timestamp_column > $1 - interval '1 hour'
AND timestamp_column < $1 + interval '1 hour'

The database return a error saying the the operator timestamp > interval
does not exist.

Either the query

SELECT * FROM table WHERE
timestamp_column < $1 + interval '1 hour' AND timestamp_column > $1

Does not work

The $1 value is a timestamp (like now() for instance).

But the query
SELECT * FROM table WHERE timestamp_column = $1 OR (
timestamp_column > $1 - interval '1 hour'
AND timestamp_column < $1 + interval '1 hour')

works as expected.

It seems that the analyzer cannot guess the value of a prepared statement
combined with an interval. For my test i'm using PHP without PDO.