Ability appears as if you can cast it when oom

At least once or twice a day I come across a bug where the ability button would glow as if I had the mana to cast it, when in reality I didn't have enough mana. When I attempt to cast it, that's when it would register that I'm oom and the button would go dim.

I only ever experience this when I cast an ability, either the one I want to use or a different one, and use the last bit of my mana, and the ability I attempt to use is on cd during that time.