Delete the last line with two backspace, it will produce the following error in the console:
Uncaught DOMException: Failed to execute 'appendChild' on 'Node': The new child element contains the parent. at CKEDITOR.dom.element.append (https://ckeditor.com/assets/libs/ckeditor4/4.14.0/ckeditor.js:97:300) at l (https://ckeditor.com/assets/libs/ckeditor4/4.14.0/ckeditor.js:1132:15) at a.<anonymous> (https://ckeditor.com/assets/libs/ckeditor4/4.14.0/ckeditor.js:1147:282) at a.c (https://ckeditor.com/assets/libs/ckeditor4/4.14.0/ckeditor.js:10:70) at a.<anonymous> (https://ckeditor.com/assets/libs/ckeditor4/4.14.0/ckeditor.js:11:433) at a.CKEDITOR.editor.CKEDITOR.editor.fire (https://ckeditor.com/assets/libs/ckeditor4/4.14.0/ckeditor.js:13:97) at CKEDITOR.keystrokeHandler.g (https://ckeditor.com/assets/libs/ckeditor4/4.14.0/ckeditor.js:249:395) at $.c (https://ckeditor.com/assets/libs/ckeditor4/4.14.0/ckeditor.js:10:70) at $.fire (https://ckeditor.com/assets/libs/ckeditor4/4.14.0/ckeditor.js:11:433) at HTMLBodyElement.<anonymous> (https://ckeditor.com/assets/libs/ckeditor4/4.14.0/ckeditor.js:68:412)
Type of report
Bug
Provide detailed reproduction steps
Create a two level list as follow:![image](https://user-images.githubusercontent.com/10050616/76768437-4b59f580-679b-11ea-8ebf-ad37359f526a.png)
On the empty sublist item, add an ordered list:![image](https://user-images.githubusercontent.com/10050616/76768529-6c224b00-679b-11ea-89d4-e456460b4519.png)
Delete the last line with two backspace, it will produce the following error in the console:
Uncaught DOMException: Failed to execute 'appendChild' on 'Node': The new child element contains the parent. at CKEDITOR.dom.element.append (https://ckeditor.com/assets/libs/ckeditor4/4.14.0/ckeditor.js:97:300) at l (https://ckeditor.com/assets/libs/ckeditor4/4.14.0/ckeditor.js:1132:15) at a.<anonymous> (https://ckeditor.com/assets/libs/ckeditor4/4.14.0/ckeditor.js:1147:282) at a.c (https://ckeditor.com/assets/libs/ckeditor4/4.14.0/ckeditor.js:10:70) at a.<anonymous> (https://ckeditor.com/assets/libs/ckeditor4/4.14.0/ckeditor.js:11:433) at a.CKEDITOR.editor.CKEDITOR.editor.fire (https://ckeditor.com/assets/libs/ckeditor4/4.14.0/ckeditor.js:13:97) at CKEDITOR.keystrokeHandler.g (https://ckeditor.com/assets/libs/ckeditor4/4.14.0/ckeditor.js:249:395) at $.c (https://ckeditor.com/assets/libs/ckeditor4/4.14.0/ckeditor.js:10:70) at $.fire (https://ckeditor.com/assets/libs/ckeditor4/4.14.0/ckeditor.js:11:433) at HTMLBodyElement.<anonymous> (https://ckeditor.com/assets/libs/ckeditor4/4.14.0/ckeditor.js:68:412)
You can reproduce this bug on the demo page: https://ckeditor.com/ckeditor-4/demo/