Not sure where to post bugs, so I'll kindly ask a fellow forumer to repost this in the appropriate site.
Nature of Exploit: Load / Save bug
I made an elf sorcerer, picked two spells (magic missiles and shield), saved the game, quit to main menu, then made a conjurer (human) and picked three spells (armor, find familiar and sleep), then made its own save.
Reloaded the sorcerer and voilà: sorcerer now knows magic missile, shield, armor, summon familiar and sleep. Proceeded to ankheg fields to test if the game would let me pick more spells than five; abused sleep, farmed ankhegs to level three, picked a sixth spell (blindness). Opened the spellbook and there it is: all six spells available.
Haven't tested if this also works with leveled mages with meatier spellbooks. If if does, you can literally have a sorcerer with any number of spells per spell circle as you want.
This needs fixing ASAP if you ask me, but it's also kind of an awesome cheat / glitch.