I don't know if this has been reported or not. But when you use tempest and have pips built up and tempest fizzles, you lose all your pips. It wasn't like this before the updates that I remember. Hopefully it can be fixed.
I'm bumping this topic since this has happened to me a few times now.
Burned 14 power pips on what I assume was a fizzle since it didn't show the fizzle graphic. The spell apparently fired off since I lost all of those pips but no damage was done so we have a problem of a spell firing off but acting like it fizzled so you lose both the spell and the built-up pips.
Can we look into this please into this since this is getting to be a very frustrating problem.
This bug doesn't only happen with tempest, but with any spell that hits all enemies. Basically what triggers it is when the mob you target with the spell gets killed before your area spell is cast. In this case your turn is skipped and then at the beginning of the next turn all the pips that spell would have used are gone. I agree that this is very frustrating when it happens.
Until this bug is fixed, I would suggest that you make sure to target a mob that you don't think will be killed by any other players. Or you can ask the other players not to attack the mob you are targeting with tempest (if they go before you).