G 10 goes back to Canon

I have had this camera for about 2 months now, and I am moderately pleased, but had to return it due to a fault

About 5 % of my shots are underexposed by about 3 to 4 stops. Not a subtle problem, the shots are almost black. Interestingly, if I shoot in continuous mode, I can take a series of 10 JPGS, the first, say, 4 will be OK then I will have 6 almost black images without any change in the shutter/aperture combination. The histo is pushed to the right suddenly by about 4 stops.

For the life of me, I cant see why this is happening, and neither could our local service agent.

Has anyone else experienced this ?