Somewhere along the way it was discovered that many of the kit class spells, such as Boon of Lathander and Helm Seeking Sword, would cause Baldur's Gate II to crash when scripted with the trigger 0x4031 HaveSpell(I:Spell Spell). This latter also proved true with several of the spells added by the expansion Throne of Bhaal. A work around for casting the spells was developed by one or more of the talented scripters, so scripting life continued unabated.
I am not 100% certain, but I believe it was Dave Gaider and Mark ?, employees of BioWare, who discovered how to fix this problem. The problem was that the level of the spells was incorrectly defined in their .spl files. Instead of being set to 1, they were set to the equivalent values of their mage or cleric counterpart spells. In short, probably a copy/paste error.
At some point it was, I believe, Vulgar Zildrah who compiled the fixed .spl files into a single package, Repaired_Innate_BG2_Spell_Files. Then sometime later, I came along and fixed some of the ToB spells and compiled them into another package, More_Modified_Innate_ToB_Spell_Files.
Scriptable Spells combines the two packs into one and uses WeiDU to install and modify the level of the spells.