During a level up a character gains new spell slots without any kind of learning.The learning of new spells has been left out and thus the character does not truly advance in his base class.
Outside NWN the idea of this mechanism is far from unclear, as it has been gradually clarified in numerous sourcebooks to include the following:
The above has been worded in different ways throughout the books, started from the simple phrasing:…the character gains new spells per day (and spells known, if applicable) as if she had also gained a level in a spellcasting class she belonged to before adding the prestige class. She does not, however, gain any other benefit a character of that class would have gained (improved chance of controlling or rebuking undead, metamagic or item creation feats, hit points beyond those she receives from this prestige class, and so on), except for an increased level of spellcasting. If a character has more than one spellcasting class before becoming a Example Prestige Class, she must decide to which class she adds the new level for the purpose of determining spells per day.
More recent editions show the longer, more specific explanation above this.…the character gains new spells per day as if she had also gained a level in whatever arcane spellcasting class she belonged to before she added the prestige class. She does not, however, gain any other benefit a character of that class would have gained. This essentially means that she adds the level of Example Prestige Class to the level of whatever other arcane spellcasting class the character has, then determines spells per day and caster level accordingly.
The crippled way the NWN’s script handles level-ups does not really hinder the Wizard class, as Wizards can add another page to their spell book via scroll use (this process merely takes time in this setting), but Bards & Sorcerers are castrated because of this, not benefitting at all of the increased ability unless a metamagic feat was chosen - a somewhat expensive and non-efficient way to try to compensate flaws of the game engine.
Is there some reason to prevent the spell casting development of other arcane casters than Wizards, or would it be plausible to just fix the flaw and let the community to enjoy the real potential of all arcane classes?
The problem is easily solved by DM adjustment, if the immersion of DnD rules in this context - and equality between arcane casters - is desired.
Any opinions? Moves for, or against?
Quotations from DnDWiki.com for the sake of convinience.