Here it is:

The spell effect came from the Molten Core mob 'Baron Geddon'. It's similar to an AoE 'Curse of Doom'. They managed to get their Felhunter hit with it, then Dismissed it.

Blizzard wanted Warlocks' Pets to keep any debuffs when dismissed, to prevent any unsummoning/resummoning to clear debuffs.

All he/she had to do is resummon it, and watch the timer go down.