Permission keeps reverting from edit to view

I changed someone's permission to a folder to 'edit' and it gave a message that it saved the changes:


But it keeps reverting to 'view' permission.  I tried this on person and group accounts...same result.  I tried this on a different library, same result.  I tried this on a different site -- which worked as intended.  Is there a reason a particular site won't allow assigning edit permissions?  It worked when I assigned 'full control' but assigning 'edit' permissions doesn't work and just assigns 'view' permissions.  The library permission is not inherited.