I tried to reproduce this issue but I could not.
I used the Formatting toolbar plugin and the Daemonite Material Theme and here’s what I see:
Make sure that:
- Your Discourse install is on the latest
- You have the latest version of the the plugin
- The theme is updated.
If the issue still persists, it would be a lot easier if you can share a link to your site so that we can check and see what’s wrong.