There's no clear pattern to how it's being used, no wiki page to explain what it's for, and the name sounds subjective. No sense requesting an alias to "invalid_tag" because apparently we're not doing that anymore, but I could at least send it to the Zero Post Zone if that's all right with everyone.
Topic: Request to remove tag: "proper_proportions"
Posted under Tag/Wiki Projects and Questions
you can just purge it yourself. the tag was seemingly only ever added by a now deleted user several years ago and an inactive user over a year ago, and it currently only exists on seven active posts.
You don't have to now, I did it lmao