I've seen this several times, mainly with AIs that use Explosion or Steal.
Instead of targeting the shield I have in play and delivering the final attack, they will target other permanents. Namely, Feral Bond, Hourglass, etc.
Maybe this should be fixed? Just wondering as any player worth their salt would go for the killing stroke instead of prolonging the match and granting their opponent a reprieve to possibly win.
Also, when an AI plays a virus or retro virus, it will activate the card's ability without a target. I can see this if a Boneyard, Graveyard or Bonewall is in play but wasting a creature like that purely to activate it's ability is silly.