When Adding a category to a tab, another category may be replaced

[RealRaven2000]

When adding a new category on the "Set Category" dialog, under certain circumstances an old Category my be removed:

Expected outcome: the old category "Green" should remain selected and Blue should be added and selected also.
Observed behavior: Category "Green" is deleted and only the new Category "Blue" selected.

This behavior can only be observed if no other Tab is member of the old Category "Green".

[RealRaven2000]

Explanation of this unexpected behavior:

Categories are stored as tab attributes (not in separate entities). When the new Category is added, QF deselects the existing Category "Green", adds the new Category "Blue" to the tab and then rebuilds the database. Since "Green" does not exist in any (other tab) it will not be listed anymore. The solution would be to change this behavior and retain the old Category with in the current tab while adding the new one.

[RealRaven2000]

Fixed in 5.9, released on 30/03/2022