backward compatibility of flow from 6.5 to 6.1

I implemented a flow service under IS 6.5. When I install its package under IS 6.1 I get strange results (e.g. the service has empty content, and its package cannot be deleted with Developer)

I presume that flow services are not backward compatible from a later release to an earlier one. Is this true?

BTW, the service does a test of the WmFlatfile package.