Why does Delta2D restore deleted spots when I am editing other spots?
To understand this phenomenon, it is necessary to peek behind the scenes of Delta2D:
When you delete a spot, Delta2D does not really delete it in the sense of removing it. The spot only gets the status 'cancelled', which means it will not be shown any more, it will be excluded from the normalization set of spots, and it will not be mentioned in the count of spots you can find in status bars or reports.
This is necessary to notify Delta2D that you do not want to have a spot right there, even if Delta2D would detect one with the defined detection parameters. When you now place an edit marker nearby, this triggers a new local detection process with your edit marker as guide line. If this redetection finds a previously cancelled spot, this spot again will get the status cancelled and so you usually don't have to delete this spot every time.
"Usually" means, that of course there is an exception: If you set an edit marker on a cancelled spot, Delta2D gets into a conflict: You cancelled the spot, which means you don't want to see a spot right there, and you set an edit marker, which means you do want to see a spot right there. In such a situation, an edit marker will be weighted higher, the cancel status of this spot will be removed and a spot will be detected.
If you remove this edit marker later on, the spot will be re detected in the same manner as it was before it was cancelled.
Depending on the size, shape, number and place of your edit markers, this can affect spots in the neighbourhood as well, which sometimes looks like 'deleted spots have been undeleted'. You can observe better what's going on if you make cancelled spots visible: in the DualView menu choose: "Spots -> Show Cancelled Spots". Cancelled spots will be shown with a dashed line, so that you will be able to identify them at a glance.