You have SM and IDM integrated. You have discovered that on any change to the IDM configuration (i.e., importing Directory.xml to extend the schema), this somehow overwrites SiteMinder's LDAP User DN Lookup directory configuration, breaking authentication and authorization for every integrated application until the settings can be manually reset.
How can it be that a change to an external system overwrites SiteMinder settings?
Refer to the "REST API Reference Documentation"