I had just answered a post and pressed "Submit" only once. However, my resposne was shown twice after the submit. Therefore, I have deleted the second reply and found out that both are being deleted. This is the post.
It looks like a "refresh" glitch, I've also have the case happening when the answer was sent after a bit of time.
[edit: finished answer after hitting submit accidentally...]
It is a bit annoying, but recoverable at least. I thought that I am not the only one. Not sure if I have not reported this myself already.