I posted a comment on this answer fairly soon after the answer was posted, then immediately edited the comment to provide a specific counterexample to the assumptions in the post. (There is a 5 minute limit from the time of posting for editing comments.)
Post-edit, the comment was a fairly long and detailed (within the length limit for comments), especially compared to the shorter initial version. As soon as I clicked "Save," the comment completely disappeared, with no warning whatsoever! Why is that?