Toolbars turn on or off depending on the files type, but try to keep their same locations. Turning on a toolbar in a drawing, for instance could "push" the location of a toolbar used in drawings and parts so that when you go back to a part, the toolbar is moved.
The easiest way to stop the movement is to open a part, assembly, and drawing at the same time. Find good homes for each toolbar and switch between each file type until the movement stops.