I have a collection of calendars on a Davical server.  They all appear as separate calendars in a collection in the tree view.
KOrganizer often de-selects my calendars for some reason, so I have to click on them to re-select them to see the events.
One time I clicked and accidentally dragged slightly, and the calendar I tried to click on was copied into another calendar and appeared as a sub-calendar.  The calendar now appeared twice in the calendar view.
I right-clicked on the duplicate calendar, and the only option available to remove it was "Delete Calendar Folder".  It asked me if I wanted to delete it, and I clicked yes.
The original calendar still remained in the tree view, but the actual calendar, containing thousands of events, had been DELETED FROM THE SERVER (which is running Davical).
After re-fetching the list of calendars in the underlying calendar collection, the calendar had indeed been deleted, and no longer appeared in the tree view.

The problem is the unintuitive behaviour.  If you accidentally duplicate your calendar, how do you get rid of the duplicate?
The first problem is that you can make a calendar a sub-calendar, which in reality isn't reflected in the calendar structure on the server.
Secondly, the only option to remove a duplicated calendar is "Delete Calendar Folder"
Thirdly that, despite asking you if you want to do this, it's not clear that this deletion will be propagated to the server.

The way to get the calendar tree back to normal is not to do any manipulation of the tree using the GUI, but to re-fetch the list of calendars in the collection using the calendar server settings in the configuration menu.

Reproducible: Always

Steps to Reproduce:
1. click and drag on a calendar in your collection to another calendar in the collection
2. select copy

Actual Results:  
You're left with a duplicate calendar that when you remove it in what seems like an intuitive way, you irreversibly delete the calendar from the server.

Expected Results:  
You're left with a duplicate calendar that when you try to remove it, simply disappears and leaves the other calendar in place.
Even if it was the only calendar in the list, I would only expect the calendar to be deleted from the tree view, not from the server (at least not without a very serious warning message).