The problem we ran into was a bit unusual and not likely to affect most Steem users. We were claiming some of the "free account credits" using a 0.20.4 wallet and also watching our RC amount on steemed (which was running 0.20.5 but apparently hadn't fully replayed). So both were reporting the wrong amount of RC being used for the transaction (and it is a super-expensive transaction that costs far more RC than any other transaction). The other issue was that some witness outside of the top 20 were still running older versions of steemd that allowed these transactions thru, which allowed our RC to go negative. Fortunately, we stopped it before it went too far negative.