FAQ 15 makes no mention of the fact that you can't delete anonymous comments that you leave in other journals. It should probably be updated with a statement to that effect somewhere. Perhaps as a new line where the FAQ switches from talking about deleting to talking about screening (italics is new):
"To delete a comment, click the button with the red "X" on it, and confirm your intention to delete the comment. The next page you see should report that the deletion was successful.
You cannot delete anonymous comments that you post in other journals or communities. Only the owner or maintainer of that journal or community would be able to delete the anonymous comment."
OK, probably worded more betterly than that, LOL, but you see what I mean. Something to say that if you choose to leave an anonymous comment, you can't come back later to delete it, but that the owner/maintainer could always delete it.