In project stage Development ValidateComponentNesting is used to check if UIViewParameter and UIViewAction are nested within f:metadata. For this, a check is performed if the current component's id equals UIViewRoot.METADATA_FACET_NAME. This is not working correctly, as the metadata UIPanel component's id is null.
The result of this bug is an incorrect warning message "The metadata component needs to be nested within a f:metadata tag." (the application works as expected).