Creation does not give option to create after winning a siege defense battle.
I made a map where I am under constant onslaught and barely defending in my castle. It is a lot of fun, but this skill that is pretty integral just does not do anything.
I am playing on the steam release version.
EDIT: I think it is caused by there not being a victory screen after defensive battles? I would also like to view the outcome of the battle, how many units I lost etc, it is just not there.