I wouldn't be surprised to see something like the OP describes happen

I don't think you thought about this carefully. Going from "(+0 -2)" to "(+0 -1)" would require votescast to be decremented. We never decrement it.

What does happen sometimes is that updates get lost. If both parts of the update got lost, then the reputation display simply wouldn't include that vote. It would not go "backward".

If only half of the update got lost (only votescast getting incremented or only reputation getting inc/decremented), then you'd see something like "(+0.5 -2.5)". People would remember seeing such a thing so I don't think that has ever happened (which makes sense, considering how the node cache works, such would be quite unlikely though perhaps not completely impossible).

I was thinking of three downvotes; one initiated by one server while two others happened on the other server. At this point the OP sees -2 (perhaps the OP was even one of the two downvotes); once the first server updates the node record it is "decremented" to -1.

I agree that (rather rarely) someone casting a vote could see it reflected in the resulting display, while someone else votes and their update overwrites your update so that when you next refresh the node, their vote is reflected in the reputation while yours isn't (which, in many cases, you wouldn't be able to tell).

I think it would be extremely rare for two votes to happen so quickly that both those votes get 'lost' by a subsequent vote. On such a rare occasion, I think it would be even more unlikely for those two votes to show up anywhere together (it is hard to have a "race" between three votes while not having a "race" between two of the votes -- if two votes happen on the same sever, then they happen far enough apart for a page to be served 'between' them).

So I doubt we have races between three votes very often (I'd guess twice in a year would be unlikely). I doubt such has ever resulted in two of the votes being reflected in a reputation display before being 'lost'. I doubt 'lost' (single) votes get displayed to other than the person casting the vote very often.

The original node was describing seeing 'lost' votes several times and I get the impression that it wasn't on nodes that the author voted on. And that is something I consider to be way beyond "unlikely".

- tye