[scharfis_brain]

deshaker 'only' applies global motion compensation to the frames. This means that only the whole frame is being moved.
This is also done with previous and future frames.
But every movement that does not equal to the whole frames movement - I call it differential movement - will most likely produce some weird artifacts at the compensated borders.
Of course, one could write algorithms that will do local motion compensation on the frames that are being used form border filling. but that would slow down the process even more.