Steps to reproduce:
- Edit any wiki page in normal mode, like https://en.wikipedia.org/w/index.php?title=Wikipedia&action=edit§ion=1, with CodeMirror on.
- Select two words in different places: select one word with the mouse, press Ctrl (⌘ on Mac), select another word.
- Press B icon on the toolbar to bold them.
Words become enclosed in ''', like this:
Both words are inserted into both cursor positions, like this:
Browser: Chrome on Windows 10.
The same applies to the <charinsert> tags.
Note that the new wikitext mode doesn't seem to support multiple cursors.