0.4.0c - Lingering Illusion bugged interaction w/ Efficiency II

Recreate it:

Step 1. Lingering Illusion has a cost of 10 mana.

Step 2. Efficiency II can be put into Lingering Illusion.

Step 3. 10 mana cost does not change

It does not look like a tooltip bug. My mana still costs 10 when I use the ability.