I am using Citizens 2.0.15, their very latest Dev Build with Spigot 1.8.3.
I try and make a cat NPC sit and it does not work, I have been ensured by the Citizens Team that it is a Spigot/Bukkit issue, see here - https://github.com/CitizensDev/Citizens2/issues/286#issuecomment-84558079
Another bug, I cannot make Wolves angry using Citizens also, see here - https://github.com/CitizensDev/Citizens2/issues/291