When I tried our test suite against 9.2.1 one of the tests failed,
it looked really strange, the query had returned a row which could
impossibly match the WHERE statement.
I heard on #postgresql this bug has already been reported.
If helpful, here is a simple test to reproduce the problem:
http://pgsql.privatepaste.com/6429e8a200
From what I understand from the discussion, this "bug" or behaviour
has been around for quite some time, dating back to 7.4,
perhaps not exactly the same in all major versions though.
Would you recommend me to rewrite all queries of this particular
type, where you have COALESCE in the WHERE statement,
as a precaution?
We haven't migrated to 9.2 yet, but perhaps there is a risk
similar queries can render the same problems even in 9.1?