A WoG bug:

When a commander with Block ability active (Defense + Speed) attacks a stack processed with Fire Shield, there is a chance to trigger Block with the Fire Shield damage. Once Trigger, the Block animation would be played on both the commander and the stack with Fire Shield.

It seems to be a visual bug only. The correct way would be to play the animation only for the commander. Although it is also questionable whether Fire Shield could be considered as Physical damage that can be blocked by the commander.

Btw, I recreated Block ability with erm. I think this script has the perfect behaviour imo. It seems to me that the timing for triggering commander's Block is like at MF1, while I coded my scirpt with OnStackToStackDamage.