Weird. I personally consider a modified timestamp more confusing/worrying than an old post being on the front page, as the former modifies something that should be immutable, while the latter doesn't.

Edit: Semi-related issue for comparison: one time, a contact DMed me on Discord to ask where a certain event was going to be held. Before I saw the message, she found the answer through other means and thus "helpfully" deleted her message to me.

Same problem: that actually makes it more confusing because I see inconsistent state: the notification lives on in my phone, but it's no longer present in the chat history. Better to just say "never mind" than to modify history.