If it's not global, just make sure you select the correct Default Dialog in the sidebar menu. If it is global, it ceases to function, and then from this thread:

http://www.larian.com/forums/ubbthreads.php?ubb=showflat&Number=520352#Post520352

Roguelike mentions the fix is adding:

IF
DialogStartRequested(_Char, _Player)
THEN
StartDefaultDialog(_Char, _Player);

to the KB section of the dialog script in Story Editor.