Base class: Shadowkeeper?

Hello,
What does "Base Class" refer to in Shadowkeeper/EE Keeper?
I've made a multiclass mage/cleric and simply removed the "base class" in Shadowkeeper. My PC is still a mage/cleric, but with the effect that he now receives 1 extra spell slot per level as if he is a specialist mage.
Do anyone of you know the technicals of Shadowkeeper/the game what this actually entails?

Thank you!
What does "Base Class" refer to in Shadowkeeper/EE Keeper?
I've made a multiclass mage/cleric and simply removed the "base class" in Shadowkeeper. My PC is still a mage/cleric, but with the effect that he now receives 1 extra spell slot per level as if he is a specialist mage.
Do anyone of you know the technicals of Shadowkeeper/the game what this actually entails?

Thank you!
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Comments
An up to date (EE) version of the game won't give you specialist bonus spells for having kit zero, but it will still give you the 15% spell learning penalty that specialists take outside their school. All recruitable versions of Imoen, in both BG and BG2, suffer from this.
I don't know the code details, but I suspect this comes from legacy BG material; specialist mages were the only kits in the original BG, and some things slipped over when the kit system was greatly expanded in BG2.
I've the latest EE Keeper, but I'm still receiving the extra spells per day for removing the base kit line.