This may have been discussed on MSO but I don't go there any more, so I wouldn't see it and don't believe we should have to search elsewhere for answers relevant to this SF.
It happened again today but certainly not for the first time that I cast a vote to close a question (which question is not really relevant), in this instance it was to move it to SU. Sometimes that question is later edited or, as happened this time, someone found a dupe and the vote would have been better cast as close it as a dupe, rather than to move or close it. Other times the edited question changes things enough that I wish I could retract the vote altogether.
Is there a reason why this hasn't been implemented? I suspect it's a design decision rather than an oversight, although I can't immediately see the reasoning for it.
If it really was an oversight, can we please have it implemented?