Whenever I'm playing as the Atlanteans and I upgrade a villager to a hero while its building it will sometimes stop and never return to building unless I task it to do so. The same thing occurs if the villager has been tasked to walk somewhere and you upgrade it to a hero.
It's not that big of a deal, but I usually mass select vills before turning them into heroes so that I don't have to select them one by one (that really wastes time).
Just let me know if anyone else has had this problem.