Export from Storyboard to Toon Boom (layers problem)

When I export from Storyboard to Harmony (settings “Original scene”, NOT “Nest panels in Symbols”) all the layers are visible in the Toon Boom file, even if they are set invisible in Storyboard.
How can I fix that?

I know that this doesn’t happen when I activate “Nest panels in Symbols”, but nesting is rather impractical for my purposes. Unless there is a possibility to later “ungroup” them in Toon Boom again. (Is there?)