Suspicious downvotes on questions

I have noticed a suspicious pattern of downvotes on questions.

Here is a typical sequence of my actions when I post an answer on another user's question:

• I upvote the question
• I edit the question
• I post my answer

Within a few minutes of posting my answer, I often notice that the question has a new downvote. In most cases, it is the only downvote on the question. I confirm this by looking at the question timeline.

I can not see the exact timestamp of each vote on the question in the timeline, but it shows 1 upvote (mine) and 1 downvote on the day I posted the answer.

Although the timeline does not show the timestamp, it can be seen in the "Post" view in the reputation tab of the poster if you hover the mouse over the entries:

• My upvote was at 2025-01-04 11:57:50Z
• Someone else's down vote was at 2025-01-04 11:59:24Z, less than 2 minutes later.

(Courtesy of user @Martin R)

This has happened many times.

It happened today on this new question, posted 16 hours before my answer:

Basic, general lexer for a programming language

I realize that by editing a question and posting an answer, the question is bumped and receives new attention. This could account for another user seeing the recent activity and voting. However, it always seems to be a single downvote on questions that are otherwise well-received. It is usually the only downvote on a question with multiple upvotes.

I suspect a bug, as opposed to another user casting the downvote, because the downvote seems automatic. It seems unlikely that there is another user (or a very small number of users) who is that vigilant.

I have also noticed this on old questions that I have answered/edited/upvoted. Here are other recent example questions:

Motor control PLC in Python

Maximum total reward of a game

Conway's Game of Life with turtle graphics

I mentioned this recently in the 2nd Monitor chat, and Moderator @Peilonrayz asked if I would gather a few example questions for escalation to a CM.