When a course's short name is very long, it will push the dropdown item width out and break layout.

To recreate, make a new course with any course name you want, but make the short name very long (get as close to the 100 character limit as you can to really see the issue).

Now, go to the course and access the 'More' dropdown. Notice that the dropdown menu is very wide and most likely exceeds your page width.

This issue can be easily resolved by removing the unnecessary mention of the course shortname in the 'unenrolme' string. The item in the dropdown menu would then read 'Unenrol me from this course'. 

This issue is related to MDL-76947 and has been commented on with the proposed solution.