Earlier I wrote and posted an answer to this question:
Order of prepositions "of" and "by"
Somehow, in the process of making one or two edits almost immediately, the flag under the Downvote triangle changed colour, with the mouseover message "Unsave this answer".
There is nothing in this site's help information to explain this feature.
So my questions:
What triggered this flag, which has never happened before?
How is "Unsaving" different from Edit?