rails: ActiveRecord::Relation#to_sql does not match SQL executed when using includes

1.9.3p194 :009 > Todo.includes(:user).where("users.id" => 1)
  SQL (0.5ms)  SELECT "todos"."id" AS t0_r0, "todos"."name" AS t0_r1, "todos"."user_id" AS t0_r2, "todos"."created_at" AS t0_r3, "todos"."updated_at" AS t0_r4, "users"."id" AS t1_r0, "users"."name" AS t1_r1, "users"."created_at" AS t1_r2, "users"."updated_at" AS t1_r3 FROM "todos" LEFT OUTER JOIN "users" ON "users"."id" = "todos"."user_id" WHERE "users"."id" = 1
 => [#<Todo id: 2, name: "Wash the car", user_id: 1, created_at: "2012-05-02 22:15:55", updated_at: "2012-05-02 22:15:55">, #<Todo id: 3, name: "Get a spare key made", user_id: 1, created_at: "2012-05-02 22:16:05", updated_at: "2012-05-02 22:16:05">] 
1.9.3p194 :010 > Todo.includes(:user).where("users.id" => 1).to_sql
 => "SELECT \"todos\".* FROM \"todos\"  WHERE \"users\".\"id\" = 1" 

In looking at Issue #5990, @isaacsanders and I stumbled upon this issue.

We were attempting to make #pluck generate the same query that is used in the standard finder, but discovered that it doesn’t use that query. We think this is the issue at the heart of #5990.

Thoughts?

cc @josevalim @tenderlove @steveklabnik