This has finally been resolved.
Big thanks to Steve from Liquibase support (above) for jumping on a call to help debug this.
Seems the main culprits were an outdated Liquibase.jar and an improperly set JAVA_HOME. The issues were linked like this:
I downloaded the latest jar and compared the liquibase script with my own. They were mostly similar but the newer version had additional code near the bottom. What is important is that the newer jar sets the JAVA_PATH environment variable based on your JAVA_HOME.
Bottom line: use the latest liquibase script and ensure your JAVA_HOME is set.
Jonathan