Cannot edit events more than once per calendar page view

Steps to reproduce:

• click on any event in the calendar overview (or create a new one), go into edit mode for the event by clicking the "Edit" button in the event dialog,  and then click "save"
• then choose another event (or the same one), open it and click "Edit" and "Save"

expected result: in both steps the event dialog closes, saving the changes.

actual: when clicking on the "Save" in the second event, nothing seems to happen.
(The is a red warning bis in the lower left corner of the page saying: "The content cannot be saved because of a CKEditor internal error. You should try to copy your important changes and reload the editor.The content cannot be saved because of a CKEditor internal error. You should try to copy your important changes and reload the editor." - however this is not visible with the dialog open.)

There is a javascript error in the console:

   [CKEDITOR] Error code: editor-element-conflict. Object

Unknown macro: { editorName}

which links to https://ckeditor.com/docs/ckeditor4/latest/guide/dev_errors.html#editor-element-conflict

It seems the previous CKEditor instance is not properly disposed.

The workaround from the user point of view is to reload the page every time an event is saved. Very inconvenient, of course.

I think I had not observed this behavior with XWiki 15.10.8, but I need to check.