I understand from my source that Rachel (Christmas Present) and David (Scrooge) stayed in character as long as they could. The wand often malfunctions, alternating between not working at all to making fireballs that are larger than necessary. This time, it shot upstage and light the curtains in Scrooge's bedroom. The curtains glowed for a moment before bursting into flame:
Scrooge: You burned down my house!
They continued as stage hands extinguished the fire, but when they spun the set, the smoke became too distracting and the decided to close the show.
I understand the wand will probably just be a wand from now on, but I love a good ad lib! I think the challis that drops is usually the worst malfunction in the show.