DropPrimaryKey - Fails in Postgres

I came across an issue in DropPrimaryKey change tag.

<changeSet id="me" author="updatePrimaryKey">
<dropPrimaryKey catalogName="sn" schemaName="sn" tableName="table_name"/>
<addPrimaryKey schemaName="sn" tableName="table_name" columnNames="column_name_1"/>
</changeSet>

When I run this change set liquibase API creates a function __liquibase_drop_pk with a single INPUT Param for table name.

It fails to honor the schema name I pass in.

create or replace function __liquibase_drop_pk(tableName text) .

Any workaround guyz!!!

Cheers,
AP.