The inability to add a DQA vote when prerequisite conditions (ie, >1 media) aren’t met was a feature request that has been added:
https://forum.inaturalist.org/t/prevent-dqa-voting-when-pre-requisite-conditions-arent-met/49859/23
However, it does seem like this
would mean that the downvote for single subject wouldn’t be grayed out, so I’m a little confused. I do think that if an observation is edited to only one photo, then the DQA vote could be dropped, though I suppose there is a small potential for abuse (eg, a person could edit to only one photo, then add the others back). But this seems really unlikely.