I think the design of the Sharpen skill was deliberate. Unlearning and relearning the skill to get the best effect would become quite costly if used too much.
The ability to learn the same skill on different slots was deliberate. For some skills this does not make sense, with others it can (ie you may want two different fire spells, one with low mana costs but low damage for weaker enemies, and another with higher damage and mana costs for stronger enemies).
While some kind of check is possible, eliminating accidental duplication while not restricting deliberate actions would be difficult to implement.
I don't recall if they said the summoning doll fix was in the next patch, but it should be near the top of the list, anyway.
