Hi!
For the sake of this example, consider that a scrum team uses story points and for some all PBIs have 10 story points.
During Sprint1, the team had selected 2 PBIs, one met definition of done, and the other was "95% done".
So, the "correct" behaviour is to move it back to backlog.
But then, on the next sprint, the team decides to choose 2 PBIs + that one left undone, since it's just 5 minutes of testing.