Early game I got a Hailstone Staff and gave it to a hero who is defending one of my cities.  But when the city is attacked it ALWAYS acts as if he wasn't there.  He's not on the combat screen, doesn't get any XP, nothing.  This is on "hard" difficulty, and hard enough without champs  skipping out when I need them  

Its the staff, not him.  If I sell it and buy other stuff he defends the city just fine.  But also, if he and the garrison move outside to attack it works fine.

Here's a save game I used to test this      http://dl.dropbox.com/u/8928343/QuickSave-hailstone.EleSav

I've loaded this 5 or six times to test different combinations, so I'm pretty sure.  If you just hit next-turn, they will attack in 3 or4 turns.

I also had the bugged defense at least a least once before the save too.