I just used a Tarlis codes artifact on a damaged TO Hyperseeker and instead of removing 10000 shields as per the effect description (Tarlis Codes : Shield -10000) its added it on

Combined damage by attackers is 64151 but its shields are at 35849/90000, only 54151 damage

The Tarlis Codes decreases the maximum shields, it doesn't just do damage to the shields in the normal way.

As Ferrus said, the Tarlis decreases the shield capacity by 10k. So in your example, the PRE-Tarlis shield status would have been 35849/100000. POST-Tarlis is 35849/90000. That being said, I do have to agree that it's a little wonky since NPC shields don't recharge. Any time you've already attacked a TO NPC before using a Tarlis, it's a waste. Part of the reason why I still have 4 of my 5 Tarlis code artifacts.