This is a three part issue.
#1 Right now the SampleData example data sources in Report Designer are JDBC based, so when publishing to the platform a raw connection is created for each report execution vs. using the connection pool.
#2 The platform uses it's own method for connection pooling vs. JNDI, so that should be used when publishing, otherwise SampleData won't exist as a valid data source. This will require changes to the platform-plugin project.
#3 Finally the local and MySQL versions of SampleData should be removed from the report designer distribution that is bundled with the platform.