I upvoted a post that, after some time and investigation, happened to be incorrect and misleading. Cf. my question "If prepend is not part of English, why ther's no postpend, subpend? and who introduces them?"
Why cannot I change my vote?
Can it be changed?
Casting a downvote on mentioned above post produces pop-up with yellow background:
You last voted on this answer Feb 11 at 18:40
Your vote is now locked in unless this answer is edited (click on this box to dismiss)
I believe it is universal in all SE sites. I clicked them many times by an error or on purpose before.