My comment on this phantom/imposter answer says:

This is the second time this has happened to me, a second, identical copy of my answer appears, and I seem to be open and active when I return to this tab. I see it open, and click save before noticing that it is a phantom/imposter post. In this case I was in the review cue (sic, it's "queue") in another tab at the same time, though I'm not sure if that's related.

I'm using the Chrome browser with several tabs open, but I am now absolutely sure that I never clicked the Add Another Answer button.

I thought I'd posted a question here the first time it happened to me, but I don't see it now. I'll see if I relocate the first double-answer (roughly a year ago).

question: How to make sure this doesn't happen again? It's not at all a major problem, I don't notice any adverse effects besides the poor aesthetics/optics of having a second, deleted answer.

I haven't added the bug tag yet since I'd like get to the bottom of what's actually happening. The bug tag can sometimes attract a status-bydesign labeler, who might clear up bugs by finding a plausible rationalization for the behavior, and thereby "solve" the issue prematurely.

edit: I remember that when I tried to save the phantom/imposter answer, I was presented with a Captcha and asked if I was a robot. I hadn't logged out during that brief span, so I'm not sure why. I believe that I dispensed with it by reloading the page. I can't remember exactly, but I didn't engage with it.