The reason is a slight inaccuracy in coordinates sent by the tracker. It is absolutely normal for any type of equipment. This inaccuracy is appreciable particularly at parkings. A unit stays still, however, the coordinates sent by the tracker slightly differ from each other. That is why 'stars' appear at the places of parkings.
You may want to get rid of those 'stars' to make the track look more intelligible. To weed off the stars at parkings, apply the trip detector to that track:
If you build a track in the Messages panel, the trip detector cannot be applied because that track shows all messages registered in unit's database.
Make sure that the trip detector is adjusted correctly. Additionally, you can activate the message validity filter on the Advanced tab of unit properties.