What you were expecting to happen, and what actually happened:
While you changed all buttons everywhere for the new design (I don’t very like the selection of colors, but… sigh), “Cast” button remained the same.
How often does this happen? When did it begin happening?
Since the new patch, obviously.
Thank you for letting us know that the new UI hasn’t been applied to the ‘Cast’ button in battle. I’ve reported this to the Development Team to investigate and correct.