Is that as expected that SkinnableContainer is recognized as "FlexObject"?
Yes. For the Beta2.
How an object is represented in the script is decided in the XML file. XML file which is available in beta is a temporary one as the actual XML file is not yet ready.
However this wont affect the automation of the applications.
Since the correct XML file is not available, the checkpoint feature will not show correct properties.
However when the automation is ready for release all these information will be available as applicable to the object.