Selected users (bulk) edit enrolment page misses enrolment duration field and so fails to remove End enrolment date

Steps:

1. One or more course participants have enrolment end dates / times specified in a course.
2. Teacher would like to remove these end dates (i.e. change enrolment duration to Unlimited)
3. Teacher selects the affected users, and then uses the bulk edit option - "With selected users " > "Edit enrolment details" (Manual or Self-enrolment, as applicable)
4. PROBLEM: Teacher cannot "uncheck" the end date ; most importantly - the bulk edit enrolments page does NOT feature the enrolment Duration part of the form; Thus Teacher is UNABLE to use this page for the intended purpose.

Expected behaviour: The bulk edit enrolments page should contain the Enrolment duration setting, which can be used to set "Unlimited" duration for all the selected participants.

Workaround - Edit enrolments individually for each participant using the Edit enrolment modal pop-ups. Can be tedious if many participants' details need fixing.