Check that all of your toons belong to the group "all".

I've noticed sometimes Jamba immediately notices I've changed and at other times there is a delay.
Generally this delay coincides with the server being a bit slower. Nothing you can do, if the server is slow to recognize something.
I generally press my master switch (and leader promote) key 4-5 times, just to make sure all the instances of wow get it.

Very rarely, as in maybe once a month, no matter what I do Jamba will have the group follow the previous leader.
Even "/console reloadui" does not work.
Leaving the game to desktop and re-entering the world always fixes this for me.