Steps to reproduce:

1. Go to space permissions view -> Edit
2. Add an individual user (A) and assign him/her some permissions
3. Make sure that the Anonymous group has the view permission
4. Save
5. Edit again
6. Uncheck all the permissions for user A
7. Make sure that Anonymous has the view checkbox checked
8. Save

Result:

• User A disappears from the permission tab
• Anonymous group lost the view permission even though the checkbox was check before submit

Expected Result:

• User A disappears from the permission tab
• All the other permissions are set according to the checkboxes in the edit permissions view

This is just one of more vectors that causes the anonymous group to lose view permissions. It happens "randomly" with other editing steps, but this one is easily reproducible.

Justification for the critical priority: when this bug occurs, space becomes visible only for registered/privileged users. In some cases it might take days or weeks before someone notices the invalid permissions and corrects them. In the meantime the space is "gone" for the anonymous world.