After playing a few hours as a mage, I got killed fighting in the bubble in Arlathan forest. When I re-spawned, my character was reset to warrior as well, including warrior items. All the saves show them as warrior now, including the character profile. Pretty cruel punishment for messing up. There was another character saved on this account too that was a warrior.
So, sounds like if you create a warrior then a mage character, and swap between them at some point your second character ends up a warrior whether you like it or not.