I believe Antoine was suggesting that you suggest wording that would make it clear (rather than implied) that close was idempotent, but "This method has no effect if the file is already closed" seems pretty unambiguous to me, so I don't really see anything to do there (and presumably neither did you :)  Which means your patch here wasn't really what Antoine was suggesting.

But please don't hesitate to offer improvements in any context, solicited or not.  You just have to be prepared for pushback, because open source :)  And when shifting from mailing list to bug tracker, you may invoke a different audience with different perceptions of the problem.

Now, two alternate suggestions have been made here in reaction to your suggestion: strengthening the "this is also a specification" sense of the first sentence in the IO docs, and writing a separate section on implementing your own IO classes.  You could take a crack at either of those if you like.  Neither of these would have been suggested if you hadn't posted your thoughts on what to do and engaged in this discussion, so it is a positive contribution even if your patch is not accepted.