IP restriction and cookies

Sor

i have set in parametres Limit polls to 0, and activated vote restriction method to both IP adress and cookies.

User can't vote 2 times on same poll => that is ok

but when i try to vote on another poll, he told me that i already voted on this poll, which is not true.

Is it because of cookies restriction ? this is not normal right ?

Also can't we not use restriction methode based on MAC adress instead of IP adress, so that users from same company (so same IP adress) can vote on same poll ?

Thanks