The psychic power "inferno" last forever once cast, not only 20 seconds.
Acount name : Alpha Legion
Character : Gregorius
Adding to this:
It may be related to dialog triggers. I had this occur during the last introductory campaign mission (the one with the wave defense). I had activated the ability just prior to a dialog cutscene starting. The ability was present in the cutscene and then continued with infinite duration after the scene. I was actually able to cast the ability again and had 2 active at the same time for a brief period (the 2nd one obeyed the expected cooldown).
Did it happen in single or coop? Please also link a screenshot if possible.
I casted Inferno once starting a map, and it damaged ennemies until the end, 4 ou 5 minutes later. So it seems it's not a graphic bug.