Minor Wizard can cast spells while stunned

[Noah Buttes]

Despite having eaten 4 straight stunbatons, the wizard still gets a free macrobomb in the form of Fireball, taking me with him.

That's an extreme exaggeration.

Probably a feature, but I hate it.

You're right. Wizards being able to cast spells while stunned but still conscious is an intentional feature. If you want that to change, I'd suggest making a post in the Ideas and Suggestions sub-forum. Bug Reports is not the proper place for a feature request.