DefaultValueComputed isn't honored when column type is VARCHAR2

I'm running liquibase 3.1.1 on an Oracle DB. I have a change that creates a table with a column of type VARCHAR2(255) and it should have SYS_GUID as default value: defaultValueComputed="SYS_GUID()".

The resulting sql from this change is: CREATE TABLE person (guid VARCHAR(255) DEFAULT 'SYS_GUID()');