diffChangeLog against two simple schemas drops non-existing foreign key, resulting in error

I created two simple databases to represent authors and books. There are small differences between the two databases. (The SQL statements to create both databases are attached)

• author_id column in table books was removed.

• The table authors_books was added to serve as a many-to-many relationship.

• The {[email}} column in table authors must allow null.

• The isbn column in table books must allow null.

• An index was added to column email in table authors

There is no data in the databases, I simply created these simple tables to test liquibase.

After I created both databases, I added the PostgreSQL driver and created a liquibase.properties file to make it easier to execute the commands. This file is also attached.

The first command I did was liquibase.bat diffChangeLog to generate a diff.xml file.
The second command I did was liquibase.bat updateSQL > update.sql to generate a SQL file with the required SQL statements for updating.

In the diff.xml is a faulty dropForeignKeyConstraint on the table authors_books named fk_author_id. That constraint does not exist on that table yet (the next change in diff.xml creates it). There IS however a foreign key constraint with the same name in the table books that should be dropped, together with the author_id column in the table books, but that change is not there. It does drop the author_id column, but not the FK constraint. Of course, running the update.sql will result in an error:

ERROR: constraint "fk_author_id" of relation "authors_books" does not exist

All files involved have been attached to this issue.