Label (Text and media area) activity is special as a name is generated from the activity text that you type in. Then text is displayed on a course page with all filters applied to it. However left navigation doesn't get filters applied so name is displayed as is without UI to fix name...
 
That could be a problem if for example you use a font_awesome filter and add an icon in the beginning of label text. 

Steps to replicate:

1. Install https://moodle.org/plugins/filter_fontawesome
2. Navigate to /admin/filters.php and enable  FontAwesome icons, Apply to Content
3. Navigate to a random course and create a label (Text and media area)  activity starting with [fa-comments fa-fw]
4. Confirm that icon is displayed in a course content, but not in the navigation.