First question of 2016 is for an Airbus pilot:

I flew an A320 DEN-RNO a few days ago, and while flying through some clouds, was staring out the window at the wingtip strobes. The right wing strobe only flashed once, which is different than the usual "flash flash" that I've seen on the Airbus. Confused, I craned my neck to look at the left wing - indeed, it was doing the double flash.

From looking at the lights more closely, my hypothesis is that there are actually 2 strobe bulbs that flash one right after the other to create the Airbus double flash. On the right wing, one bulb was burned out. Is this theory plausible? As long as one strobe works, is it necessary to replace the second one before the plane can fly again?

Thanks!