Keep Losing Access to Cleric Spellbook after Nashkel Mines

I've had the above-mentioned issue pretty much persist over several installs now. Meaning all clerics in the party upon completing the Nashkel mines lose access to their spellbooks (becomes greyed out as though they weren't a divine caster). Already memorized spells are fine as are clerics recruited after this point. Can't comment on druids as I never use Jaheira, but ranger/clerics and CHARNAME can be affected, too, though it seems with less frequency. 
As the problem doesn't always occur, I'm guessing, it's some sort of variable or effect getting stuck, though I can't tell which. Comparing an affected to an unaffected cleric in Keeper, I can't see any obvious differences in their effects and locals. Global variables I just know too little about to do anything with.
Several installs, in this case, meaning different OS installs, clean game installs with different patch levels and different mod loadouts. With the mods all of them shared being NPC Project, Scales of Balance, UB, Gavin, and Xan.
I've tried reloading and restarting, single to multiplayer save transfers, killing and raising affected NPCs, booting and re-recruiting, de- and releveling via EEkeeper and completely changing their class and then back again. Nothing fixes it.
As I tend to be level five or six by the time I head to the mines and thus often have no need to check my spellbooks for quite a while, I can't pinpoint the exact trigger.  The earliest I've ever noticed it was right after getting back to Nashkel and before talking to the mayor. The latest was Cloakwood. In affected games, I can then trace it back to the after the boss fight in the mines or however far back my saves go. 
Memorizing spells through Keeper is getting a bit annoying. 
Does anyone have any idea what's causing this or how to fix it?