JRuby on Rails using jdbc postgres (8.4) ignores Default values

Question

I have a table created in a migration (only to simplify the problem) that looks like this:

create_table :test_defaults, :force => true do |table|
     table.integer   :failure,       :default => -1, :null => false
end

So, one column named failure. When I execute this rails command:

td = TestDefault.create!

JRuby fails with:

ActiveRecord::StatementInvalid: ActiveRecord::JDBCError: ERROR: null value in column
"failure" violates not-null constraint: INSERT INTO "test_defaults" ("failure")
VALUES(NULL) RETURNING "id"

whereas the ruby version succeeds with a query like this:

INSERT INTO "test_defaults" ("failure") VALUES(-1) RETURNING "id"

I'm running:

ruby 1.8.7, 
rails 2.2.2, 
jruby 1.5.6, 
activerecord-jdbc-adapter (1.1.0)
activerecord-jdbcpostgresql-adapter (1.1.0)
jdbc-postgres (8.4.702)

Suggestions are appreciated. Haven't been able to find anything helpful on google, and don't even know who to report the bug to.

Cheers.

EDIT: Ha. Seems it only happens with negative defaults. Zero and greater is fine.

EDIT2: From my answer below, it's a code problem around brackets on negative default values in postgres 8.4. If someone can suggest a way around this issue without waiting for a gem upgrade (like telling postgres to remove those brackets), it would be much appreciated.