What's up with this red upvote? I've never seen an upvoted outlined in red.

So before I even read the comment I could already see that the upvote was red. It's not a solid red like what happens when you click on it. It's just outlined. So I clicked downvote and the upvote is still outlined in red.

There's a few other comments in this thread that appear this way but the vast majority look like normal upvote/downvote arrows, meaning there's no color until I choose one.

Has anyone seen this before?