I just noticed that my Motorola Milestone does the exactly same thing yesterday.
While I take photo at ultra low lighting condition (almost fully dark) with built-in flash light, the flash light like flashing faster than the picture is taken, and result in an incomplete photo taken.
In my case, my milestone got the problem when the battery level is about 30~40%. When I plugged the powercord or charge it over 40%, the problem really gone. But if I unplug it and leave it lower than 40% (say 30%), the problem re-appeared immediately.
After doing some google search, I found that the problem most likely appear when the battery level is low (lower than around 30~40%), and the flash light will not flashing properly (not sync with the shutter).
In addition, I search from either Hong Kong forum or somewhere, many peoples claim that they don't have such problem but only a few number of peoples have (not sure if everyone test it when the battery level is low).
In Hong Kong, there is some guys even tested 3-4 milestone and both of them have the same problem (when the battery level reached 30~40%), so I don't know if it is a hardware fault or just a software bug.