I recall watching a documentary many years ago on a civillian airliner that was lost in the Andes. the airliner was basically a converted bomber, and the wreckage was found at the base of a glacier some distance from where the crash site was always thought to be. It turned out that the debris had been covered with snow which slowly got compacted with more snow over the years, and travelled with the glacier down the mountain.
It sounds like this may be a similar issue, the "crash site" has effectively moved with the ice, but whether all the remains have moved at the same rate is another question.