1. Open an article in 2017 wikitext editor.
2. From another article, copy text which only contains the bold style
3. Place the cursor at the end of a paragraph, and paste with Ctrl+V.
4. The text is not copied.
5. For as long as the clipboard contains text with bold style, clicking anywhere in the editor doesn't move the cursor, although occasionally it extends the selection from the paste point to the place you've clicked.
Reproduced in Firefox and Chrome.