The Dink Network

well for what i know it is a engine bug as i also happens with weapons if anything else but the main weapon is equipped(usually the fists). and I've seen it happen in each and every D-mod i did(and i mean them all not counting I kara Gu as that only had i weapon(if you don't count the element swapping of it) even in some non combat ones(though there it didn't aid you by free stat points) and well for me it as you probably figured isn't just for magic also purchased weapons. and sorry to disappoint Erwin but that doesn't fix it as i had it with equal amounts of spells and inventory.
and dunno with causes it but seems like a hardcode counter error in the saving system. though I'm not sure as i'm no expert nor created it.