So Hungarian legislation is not the only one assuming similar election rules in other countries.
(In this case: not all countries require registration from citizens, some maintain you on voter lists by default. So, if I had gained residence in France, I could fill out this form, vote in France; then fla to Budapest in the certain knowledge that French authorities have not informed their Hungarian counterparts and thus I am still on the voter rolls there too, and vote a second time...) *Lunatic*, n. One whose delusions are out of fashion.
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.
This is still not a reason for separate registration on separate registers.