Leech applied to Energy Shield - bugged?

I would like to know if it is a bug - here is the context:
- I am playing Druid (Oracle ascendancy)
- I use Leech with phys dmg by doing auto-attacks (it is called "Shred" when in Wolf form) and one of my rings has "Leech X% of physical dmg as Life"
- I have "Blood Magic" on my passive skill tree, so my skills are using Life as a resource to cast skills - and my Shred (auto attack) does heal/recover my Life
- I tested the leech mechanic in my (tier 15) maps with a rare belt

- I tested my leech again with the the unique belt "Soul Tether" with the important mod "excess life recovery from leech is applied to energy shield", and the "bad mod" of losing life per second is removed by the special vaal corruption
- I still gain leech from Life, my Life does fill up...

And here is my problem / the bug I wanted to report:
--> I do NOT receive even one point of Energy shield from my auto-attacks (Shred) although I am using "Soul Tether" unique belt, even if I use "Zealot's Oath" or not - the problem remains the same
--> is this a known bug? am I understanding something wrong?

I would appreciate your help, thanks.