Expectation that searching "organization = ACME" would return all users that belong to this organization (ie. have ACME in their list of orgs in the UI).
Having two users with default organization of ACME only returns one of those users too, so it's unclear what the intention of this scoped search field is intending.
Created from redmine issue http://projects.theforeman.org/issues/9855
from upstream comment I made:
The 'default organization' is a login preference for the UI but does not imply membership within an organization. I'd not expect this search to reflect the UI preference at all. IMO, not really a bug.