A) The Hungarian citizen X in France, like myself, sees a difference between "being registered" and "being listed" -- and signs the declaration in good faith that s/he is indeed not registered anywhere but in France.

B) Assuming that being registered and listed means the same, the Hungarian citizen X faces an impossible hurdle: to delete him/her from their lists, the Hungarian authorities wait for a confirmation from their French colleagues that X signed a declaration about voting there; while the declaration French authorities want him to sign is that he was already removed from the lists in Hungary...

Or, C), the rules are improperly defined in both of our sources.

_{*Lunatic*, n.
One whose delusions are out of fashion.}