It seems that the list of teachers displayed in the course description doesn't correspond to the actual list of teachers in the course.

Steps to reproduce :

• create a new course
• add several users as teachers
• check in combo list on front page the list of teachers for the course (in some cases, no teacher appears)
• remove some teachers
• check the course description : again, teachers shown do not match teachers currently enroled in the course.

This was tested on a default local installation of Moodle 2.7 as well as on demo.moodle.net (try to remove Terri Teacher from CF101, he stills appears as teacher in course description).

Edit : my fault, this is not a bug, but comes from the caching system. Course contacts are cached, and purged every hour, thus the problem. So I just didn't wait long enough (apparently, this was already mentioned in bug MDL-41042, but left open).