It can happen that a Note seems "stuck" to another Note,
so that when you try to pick up one Note to move it, they move both. This can happen particularly when you have not finished linking Notes correctly, for example when you have not waited until the hint "Link to this Note..." appeared,
indicating that you can now create the link between the two Notes.
When this happens, first click outside of the area where the two Notes seem stuck together. This will unselect them and they will no longer be highlighted. Then click on an area that belongs to one of the two particularly and drag away the Note that was highlighted by that click. Then they are separated again and can be moved separately.