Once set, I cannot unset the 'Require end reached' option of lessons.

To reproduce the problem:

• Make a lesson
• Set completion criterium to automatic
• Mark 'Require end reached'
• Save
• Open settings of lesson
• Unmark 'Require end reached', mark another option, for example 'Require grade'
• Save
• Reopen settings

Expected result:

• Only 'Require grade' marked, 'Require end reached' unmarked.

What actually happens:

• Both 'Require end reached' and 'Require grade' are marked.