Omniscience changes the casting cost of all the cards in your hand to Zero. this means all the mana that were stored in your cards will become zero. there is nothing wrong with Omniscience. It works as the text stated.
If they were, shouldn’t they all be showing to be full mana since cost is zero? That’s what happens when Hazoret’s Fury fires. The 4 four spells are pulled, changed to zero and since zero mana fulfils the casting requirement, the cards show that they are ready to be cast. I cannot say that this is or isn’t happening MD supa… it almost sounds like he’s got Baral in play. Or something with a cast and draw effect, which of course those cards drawn are post omniscience and would not be effected.
Why can’t the mana stay instead of draining them to zero when the casting cost is set to zero? It had mana before Omniscience comes into play? it’s a matter of programming. Different valuable stored for Casting Cost vs Mana store vs Maximum Mana on the card.
I agree this card works correctly, not matter how annoyingly broken this card is.
This is not an effect like others where cards in your hand cost less or cost more for a turn or for ever like with:
Harbinger of Tides, Reflector Mage, Alhammarret, High Arbiter or Quarantine Field etc. (There are other cards).
As you stated: “Each card in your hand costs 0 mana to cast. When you cast a creature, spell, or support, this support loses 1 shield.”
All mana is drained as the card costs zero.
If a card cost 16 mana for example and you have 10 already generated and the opponent casts Alhammarret, High Arbiter to make it cost 6 more. In your turn you only generate 6, so when the effect wears off the cost is reduced from 22 to 16 and therefore the card is charged.
With Omniscience this is not the case, so nothing is ever stored and 0 is well 0.