There are two bugs with the "Include enrolled users" choice in the Backup option, one serious and one minor.

Minor bug: "Include enrolled users" choice not remembered when hitting next, then previous, then next.

Steps:

1. Go to course backup screen
2. Make sure that "Include enrolled users" is checked
3. Click "Next"
   1. Verify that "User data" is available to be chosen
4. Click "Previous"
5. Uncheck "Include enrolled users" and click "Next"
6. Click "Next"
   1. Verify that "User data" is not available to be chosen
7. Click "Previous"
8. Check "Include enrolled users" option
9. Click "Next"
   1. Verify that "User data" is available to be chosen (This step fails on qa.moodle.net)

Major bug: Having default backup "Include enrolled users" choice as unchecked makes it impossible to check it

1. Edit "Site administration > Courses > Backups > General backup defaults" and uncheck default choice for "Include users"
2. Go to course backup screen
   1. Verify that "Include enrolled users" is unchecked
3. Check "Include enrolled users" option
4. Click "Next"
   1. Verify that "User data" is available to be chosen (This step fails on Moodle 2.3.2)