2D labels contain nested instances (cell fully inside another)

CellSAM sometimes returns two instance masks where one is a strict subset of the other (see red box in screenshot). In 2D, instance masks should be mutually exclusive. Is this an expected behaviour?

<img width="536" height="343" alt="Image" src="https://github.com/user-attachments/assets/6dbe4bf2-7284-4129-9ac4-47f9356f88c5" />