I just had a bug at Team level 6 or so where I hit my geek, and then he just kept going and going. He'd go into the sky, smash down, then hit a ton of enemies on his way up, and then he kept on repeating that without my interference until the game froze when I got my second skill point in the last map.
You can upgrade after winning the game. Just click one of the maps after finishing the King's Castle.
Also, it seems impossible to get all achievements if you don't get 5/5 stars in the tutorial. Maybe allow players to replay the tutorial?