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At Stack Overflow I tried to edit an answer because the suggested methods are now obsolete. So I added a warning and the related references.
The edit has been rejected with the following motivation: "This edit is incorrect or an attempt to reply to or comment on the existing post.".
I think that I've tried to update a valid answer, without editing the original content and warning the reader about an obsolete method.
Why has the edit been rejected?
Given the particular edit, it might be merely seen as a comment on the answer, rather than an additional answer in itself. I might have done the same. It is a tricky situation.
Yes, it is an update, and yes, this is a collaboratively edited Q&A. But in practice I find that anything which goes beyond a minor correction of content (like your entire addition which somewhat invalidates the answer) is likely to be rejected.
The easiest thing to do would be to leave an answer of your own with the currently correct approach. You could then leave a comment on the original answer stating that, while originally the correct answer, the situation has changed somewhat as detailed in your answer.
