In one of the frames of animation for the assembly machine 1, when the lever thing on the top left is moving left.
When it goes past the halfway point, there's a slight jerk as the entire machine moves 1-2 pixels right for one frame, then moves back. The shadow stays still though.
This is not visible in the game world, only when you are looking in the assembly machine's inventory and there's the animated portrait of the device.
EDIT: The bug is also visible on the building card to the right when you hover your mouse over the machine
