If you have Bar2 automatically filled with the Attribute @{ac}, then a Hell Hound will have 11, yes. This is because AC is calculated - generally 10 + DEX, which for the Hell Hound gives 11. Even though NPCs use @{npc_ac}, and not @{ac}, they still have the calculated @{ac} Attribute on their character sheet - you can find it on the Attributes & Abilties tab. You're right that @{ac} is the incorrect Attribute to be using for an NPC, and linking Bar2 to @{npc_ac} will give you the correct AC for an NPC. However this is not a bug - the game is just doing what it's told and assigning Bar2 to the Attribute @{ac}. Unfortunately it has no way of discerning between player and NPC tokens. You can fix the AC problem by changing your default token settings (accessed from the launch page, not from inside the game) and linking Bar2 to @{npc_ac} by default. New NPC tokens dragged onto the tabletop should now have Bar2 linked to @{npc_ac} by default, giving you the correct value. This does mean that player tokens will now have the wrong Attribute linked by default - however you should only have a few of those to adjust back to @{ac}, significantly less work than changing every NPC in a campaign. Just make sure you re-save the default token on any character sheet after you make changes to the token, otherwise they won't stick for any future tokens you drag onto the table.