This has been happening to me as well. Where I've noticed it the most is if my tempest has fizzled once prior. I was doing some damage calculation stuff and attempted to cast a tempest at 7 pips. The spell fizzled, and the next turn I got a power pip. However when I cast the tempest that turn, it only used 7/9 pips (and did 7 pips worth of damage consequently). This was not in Deckathalon btw, this was just in unicorn way on a poor lost soul. Does anyone know if this affects any other X pip spells, or is it just Tempest?