Thumbnail panel with category color bar but only 1 photo in the database

[frankdarwin]

In my productive database I find photos in the category Duplicates with a red colour bar. But there are definitely no duplicates for these photos.

To test what the reason could be, I created a new database. I have included 2 photos in this database (original.jpg and copy.jpg).

As expected, the photo Copy.jpg was recognised as a duplicate.

Then I deleted the photo Original.jpg from the database.

I expected that there would now be no more entries in the Duplicates category. But the photo Copy.jpg is still shown as a duplicate, although there is now only 1 photo in the database.

A rescan has not changed anything either.

How can this be?
What can I do so that this photo is no longer recognised as a copy?

[Mario]

The category is assigned when the dupe is found.
Use U to un-assign the image from the category when you have deleted all duplicates. IMatch does not do that for you.

[frankdarwin]

Thank You