- Enable Twinkle
- Go to https://en.wikipedia.org/wiki/User_talk:Username?action=edit
- Attempt to warn the user.
- You can't select anything from the Twinkle menu, because of a conflicting z-index.
This is quite problematic, as redlinks to non-existent user talk pages load into the editor by default. Interestingly this doesn't happen to MoreMenus.