Manaclash does not reliably shut sustains down

[Suslik]

Consider Celia(the necromancer) with with blurred mortality sustained(she will live with, say, -300hp). Let her currently have 50 mana and 20 hp. You hit her with manaclash that burns 100 mana damage and you expect one of these outcomes depending on how game mechanics treats 0mp:
1) Mana reaches 0, hp reaches -30, though sustains are preserved when reaching 0mp, Celia lives.
2) Mana reaches 0, hp reaches -30, manaclash shuts the sustains and Celia dies.

If you test it ingame you'll find out that she'll act as a Shroedinger cat - after this experiment she can either live or die depending... On mana regen. If the target has more than 1.0(?) mana regen sustains are not shut, she lives. If less, she dies. I think that's super unpredictable since you cannot even see foe's regen rate and tell if they'll survive your attack or not. So my proposal is:
- either make manaclash never shut sustains
- or make manaclash always shut sustains if resource reaches 0
- or add some tricky condition like if target would end up with -60mp after resource damage and sustains takes 40 then it shuts, if the sustain takes 80mp(more than manaclash would leave negative) it stays.

Because major problem here is unreliability. Should I attack her with manaclash to shut blurred mortality and kill her instantly or damage her further to surpass blurred mortality threshold? I attacked several times with manaclash and failed. Found out that regen was the culprit later.

Your suggestions folks?

[Suslik]

I've talked about this problem with DG long ago and he said that making manaclash always shut sustains would be OP. Well I partially agree with this, but I still think it needs some reliablity(either always, or never or some clear condition).