Spell Casting Doesn't Consider Reduced Essence Costs Properly

[adeon6]

I've encountered an issue where the game seems to ignore essence cost reductions from Grimoires when determining if I have enough essence to cast spells.

For instance, my Grimoire grants me about 58% essence cost reduction, making my Chain Lightning spell cost around 20 essence instead of its original 50. When I cast it, the reduced cost (20 essence) correctly applies. However, if my current essence is less than the spell's original cost (let's say 30), the game prevents me from casting it and plays the "insufficient essence" animation.

It seems the game first checks if I have the original essence amount before applying reductions, leading to incorrect casting behavior. Is this a known bug?