[CrystalP]

When you add a first movie with "versions manager" the poster is not set by default.
You must set your self the local poster with button "choose art"

You can but don't have to, unless you want different art for the movie group/parent and that version.

Choose Art of Versions Manager assigns art to a specific version.
Outside of Versions Manager screen, versions use the version art first or fallback on the movie art when no version specific art is set.
Choose Art of the Info dialog or the manage context menu assigns art to the movie, which acts as a movie group when multiple versions are defined.

Every idea I tried for artwork had to compromise on something because of the scope limits set for v21 but I could have missed something, feel free to suggest an alternative.