In your Management Console, export your Corporate User Store Directory.xml file. In the file should be a line that looks similar to this:
<ImsManagedObject name="User" description="My Users" objectclass="inetOrgPerson" pagesize="0" maxrows="0" objecttype="USER">
Add your additional custom classes to this line as follows, I added myClass1 and myClass2:
<ImsManagedObject name="User" description="My Users" objectclass="inetOrgPerson,myClass1,myClass2" pagesize="0" maxrows="0" objecttype="USER">
Save the file and reimport it into the environment using the update button.

Once updated with your custom classes included, normal behavior should resume.