As you can see, Goblin trio is sufficiently overcharged at over 200%:
Upon launching the expo wave, Trio's energy is set back to 100%.
During this wave, energy sapping heroes like Void and Bone were not present.
Its medusa's blue skill steal their thunder which steals 248 energy from all foes in an area around the CLOSEST foe. If not then it's a bug.
I don't know of any Medusa stealing 1,200+ energy - besides, this is prior to her getting set and firing her green...
Then its a bug and need to be fix
This is a confirmed bug. I reported it through an in game ticket about a month ago and it was confirmed as a bug then.