I have observed this twice now, but it is seemingly random and difficult to reproduce. What happens is that the enemy will attack one of my units standing on Catacombs, my unit dies on it removing the 1 mana penalty and triggering the 3 mana pool increase, and then at the start of my turn my total mana will be missing 3. This is all very odd because the order in which static effects are evaluated at the beginning of a turn before adding resources should be well-defined and consistent.
I have observed this twice now, but it is seemingly random and difficult to reproduce. What happens is that the enemy will attack one of my units standing on Catacombs, my unit dies on it removing the 1 mana penalty and triggering the 3 mana pool increase, and then at the start of my turn my total mana will be missing 3. This is all very odd because the order in which static effects are evaluated at the beginning of a turn before adding resources should be well-defined and consistent.
See the attached FLV video file for an example:
2018-06-28 03-38-11.zip
also of note; when the bug occurs, it also manifests on subsequent turns. so you will continue to be 3 mana short.