We have done testing of this command on PostgresSQL, so in general it should work. I am guessing that there is something specific about your database schema that is causing this issue.
The code in question can be seen at https://github.com/liquibase/liquibase/blob/37e895a5696cfccf9da90d819cce62e956f2548f/liquibase-core/src/main/java/liquibase/diff/output/changelog/DiffToChangeLog.java#L634-L642
That code is looking at dependencies in the postgres objects - things like foreign keys that relate two things together. It may be that you have foreign keys in your schema that reference tables in different schemas, and the issue is that when generating the changelog, Liquibase is not gathering all the information needed for the different schemas.
Without more details about your schema, it will be difficult to diagnose further.
Principal Software Engineer
Liquibase Community Engagement
Datical, Inc. http://www.datical.com/