I accidentally clicked "Convert to answer" to a comment by another users on an answer. The comment got erased and a new answer by me, with the same text as the deleted comment appeared. That is by itself extremely stupid.
To make matters worse, I can't delete my answer. I tried clicking on "Convert to comment" and it became a comment for the question that I still can't delete (and not even edit) and I can only turn into an answer again.
In all of this, I effectively deleted another user's comment. Basically anyone can delete comments by anyone.
EDIT: It just happened again. It's too easy to click on "convert to answer" instead of "Comment" by mistake. Another thing I noticed is that if you try to convert to comment an answer without any text, it results in Internal Server Error.
Please make the comment link a lot more prominent than the "convert to answer" one, or disable altogether "convert to answer" for comments by other people! A lot of people are also posting new answers instead of comments => the comment link is badly placed.