On numerous occassion I have passed the checks for the summoning tomes. Yet, been unable to actually take the theme.
As far as Im aware, sorcerers are able to pick from a vast range of summons at creation. So I am assuming its a bug that they cannot learn a new one from the tomes that randomly appear across Ymph!
Character name: Maleken Ten'gregnos
The tomes only work for wizards with conjuration focus. Even then many of them are still bugged and unable to be taken.