A55, double-flash shooting on auto mode at night - why?

Hello all.

My daughter's relatively new A55 (bought 3 days before the A57 was released, and I knew nothing about the A57's imminent launch) currently shoots two consecutive flash-photographs at night, instead of the desired single shot.

I've run through all the settings I can think of to emulate this on my A55, though not at night-time!, but cannot. Any ideas on what setting/s might need changing?

Thanking you in expectation. (That expression always make me laugh!)

Lelly