In Epic Encounters, I've had a few bug reports of this occurring, but have also experienced it myself once, in Zandalor's house. Sometimes objects like torches, switches, and levers, along with story code functions, like ambushes and traps, will stop working entirely. Restarting the game fixes the problem, whereupon the character will say something along the lines of "I mustn't have used it correctly."
I am unsure if this is directly related to Epic Encounters, or is a problem with the base game. Have any of you also experienced such a problem?