Necro Life Tap line
 

In the original release of EQ the necro life tap line of spells could not be resisted. I know this as fact because at level 16 i was able to kill an ice giant that was trapped in a wall outside permafrost with nothing but life taps... It took me half a hr to kill him, but i did none the less.. This was later changes in patch notes, making the life tap line have a chance to be resisted. Ill see if i can find the supporting patch notes on the web.

After taking a quick look i think the change may of been made in the Dec 1999 patch/nerf update. I will try to get more info to support this.

I think it's clear they aren't going to enable bugs. The fact that you killed an ice giant at 16 should be the obvious indicator.

Perhaps not so obvious to you, however.
It was not a bug, it was working as intended and later removed during a rebalance patch. The ice giant trapped in the wall was a bug, and could be considered an exploit if repeated, which it wasn't.