I believe I've deduced the issue that's been causing my characters memory allocation problems. My very first character I had no issues spamming custom spells to quickly level all the magic skills - oft three at a time, even. My aggressive spells were target at range spells. My second character raised magic skills individually, and I started with destruction. My destruction cantrip was a center around caster type, and oddly, it had no visual or auditory effect. Spamming this spell gave me a memory allocation error within six levels. Thaumaturgy and Mysticism were also center around caster types, both offensive like destruction, and neither had visual or audio effects. Both led to eventual errors. I leveled restoration, alteration and illusion with on self beneficial spells, and max them out without issue. The take home message: if your spell doesn't do anything, don't cast it. You're lighting a fuse to an eventual useless character. If you have the same situation as me, Fixsave will turn that error into a corrupted save. So, make sure all your spells actually function both visually and audibly. I've gone through a dozen mages and three Boxer/Dosbox reinstalls - which took Arena as collateral damage. Hope this saves someone else the trouble.

Interesting, if true. I don't doubt your experience, but not sure if it will hold for others.