That bug happens to me with any faction.
If you get the message, that a faction joins the sorcerer king - you have to declare war without delay.
After a turn passes the button "declare war" is greyed out and you cannot declare war anymore.
Minor factions seem to be totally bugged, they never ever settle or build outposts in any game I play. They only walk around the map but they never expand (1.2 or 1.3 - normal or hard difficulty played)
