X64 tried
Looks pretty good.

How do you clear a semantic in the new UI? (other than hack it out of the OPF

)
In the old, UI it toggled
I like to 'prep' a book with a newer cover by renaming to 'New_cvr" and flipping OFF the semantics for both the Page and Image (this does still toggle), the have Calibre (modify epub pi ) update the metadata