Hello.

I recently restarted the game and started a play with the vodyani.

I don't know if it a bug or a new feature but my arks are being attacked while attached to a system.

Is it normal ? because with the debuff they are being killed by a one ship pirate fleet quite easily.

Cheers

Yep. totally normal. its a game mechanic. What is not normal is your ark being able to attack while attached. Arks are not supposed to attack enemy fleets while it is attached, but it is correct for enemy fleets to attack your ark while it is attached, because that is how arks generally are destroyed, giving balance to gameplay. 

If you arks where immune to attacks while they where attached, how would the enemy defeat your arks or colonize your systems? it would break the gameplay. 

Also, i will give you a tip: One time as vodianny i went attacked by pirates while i attached to a isolated system, not connected to a starlane. those level 5 fleets can beat a whole ark whit lots of military upgrades. I recommend you to defeat pirates or place defending fleets into your arks close to pirate lairs. You can also place defending fleets on arks, just increasing its CP total. 

Hope it helped! :)