It looks like there is an issue in the way a user profile is exported to LDAP (and then to Indico). Only the affiliation which is set as "Current" is exported. If this affiliation is deleted/replaced with a new one and if this new affiliation is not set as "Current Address" then the old affiliation is still exported to LDAP.
The view in the JACoW DB used for this data export is called user_person_profiles