I too have a corn like BATS says above they do produce a slurry of a poo but I have never seen this in a royal, hopefully the future ones will be solid if not there could be an underlying problem
Been googling this a bit and found a couple of independent sites reporting that a parasite infestation may manifest itself in a sloppy motion that smells really bad.
However many solid royal motions smell really bad too, so maybe not the last word and also just 'hearsay evidence' - but passing this on for what it's worth - all the best.