I have used this command:
/clone ~ ~ ~ ~17 ~9 ~-17 ~-50 ~ ~
to clone a 17x9x17 box, but instead of just copying it 50 blocks in the x-direction it moved in the z-direction as well.

as the first set of coordinates (the first corner of the box I'm selecting) are the same coordinates as the command block itself (~ ~ ~), it should (according to me) just move it 50 blocks in the x-direction. What it seems to do is take the second set of commands (second corner of the box) and move those 50 blocks in the x-direction from the commandblock (so the first corner).
So it moves it a bit (17 blocks to be exact, the length of the box) in the z-direction as well, which is just so annoying.
It would be way easier (and way less head calculating) to just take the first set of coordinates and move those 50 blocks from the command block/player, it would make more sense too.