There is currently a bug with casual games allowing players to uncheck the unranked box, certain players are choosing to abuse this to catch out unranked or low ranked players looking for a casual game, to trick them into gaining a ranked win. You have been warned, before pressing ready check the unranked box is not unchecked! Honestly greens should potentially look at warning/banning players abusing this.
I'm not gonna name and shame as that'd be blacklisting, but keep an eye on casual games and make sure if you join one, check whether the unranked box is ticked It just strikes me as unfair to target unranked players possibly even new players and trick them into having ranked losses