Nostalrius Begins - Quality wow vanilla realm (1.12)

I just came back to wow after years, first time in vanilla, first time on Nostalrius. As always, so far I've spent more time messing around with addons than playing the game.

I have a problem with AG_Unitframes: http://imgur.com/ItLDxk9

When I target myself, or my pet, i can see hp on the target unitframe like I see on the "player" unitframe: Current hp / max hp (percentage). However when I target anyone else, NPCs, players, mobs, I always see 100/100 (100%) at max hp, or when for example the target has 60% hp, it shows as 60/100 (60%). What causes this?

Also when I turn off AG_unitframes, I can't see the status text on target's hp/mana. I turned it on in Interface options. Is an other addon doing this or what? Probably it's not even AG_unitframes issue, the addon just can't get the information from the game?

Use the addon mobhealth to get hp values on target.

even with mob health you won't get hp shown up.
Only when you attack addon will calculate the estimated HP of your target.

Vanilla wow never had that thing and Nost is only server I think off to actually replicate that.
I'm not sure what to think of it.
It has it's pros and cons like everything else...

Thanks! Never knew this wasn't a thing in vanilla.