Originally Posted by
Spartin
The Unending Thirst Trait functions like this: You Death Strike, before your hit connects the healing it does is calculated and your blood shield goes up, then you do the damage. Since Blood Shield was up, your deathstrike gains the benefit of Unending thirst everytime. Whether you get the Leech benefit for anything more than a swing or two after is a matter for blizzard to decide that Blood's mastery is worth buffing or not.
That said if you get the legendary belt, Umbilicus Eternus is top tier.