Copied text is pasted with some (editor's ?) styles.
1. Open the Demo page in the Edge browser:
https://demos.telerik.com/kendo-ui/editor/index
2. Copy some words (e.g. "Kendo UI Editor") from the editor's default text.
3. Paste them at the end of the text.
4. Open developer tools (F12).
5. On the Elements tab, select the pasted paragraph and check its style, you will see <span style="display: inline !important; etc.