Switch debugging on (not sure if this step is necessary)
Create a new glossary
Set duplicates to 'not allowed'
Add an entry

Error message: Field "LOWER(concept)" does not exist in table "glossary_entries"
Stack trace:
line 508 of /lib/dml/moodle_database.php: dml_exception thrown
line 1207 of /lib/dml/moodle_database.php: call to moodle_database->where_clause()
line 124 of /mod/glossary/edit_form.php: call to moodle_database->get_record()
line 438 of /lib/formslib.php: call to mod_glossary_entry_form->validation()
line 397 of /lib/formslib.php: call to moodleform->validate_defined_fields()
line 484 of /lib/formslib.php: call to moodleform->is_validated()
line 88 of /mod/glossary/edit.php: call to moodleform->get_data()