[BUG] Graves Q Costs Too Much Mana

I noticed in a few games that I played as Graves in Patch 5.23 that when Graves gets his ultimate, his Q immediately costs 100 mana instead of the 60 / 70 / 80 / 90 it is supposed to depending on level. I tested it in many normal games and it was very consistent. In a custom game however, the bug seemed to not be present.

Is this a hidden nerf to Graves? How can this bug be fixed?