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I think that's one of their things to show that votes land instantly and calculate the amount based on your hp to simulate the effect of instant rewards. While a refresh then shows what the blockchain actually calculated it to.

Yeah, that is probably it. That is why I thought hmm it seems like votes after the downvote doesn't get affected. Live and learn lol

peakd probably added this way back when things were a bit slower cause of shteemit, back then an account couldn't even cast more than 1 vote on the same block