Magus usando o conjunto arcano para obter o vorpal

Eu estava lendo sobre a classe Magus e tenho alguns conflitos sobre como o Arcane Pool é usada.

At 1st level, a magus can expend 1 point from his arcane pool as a swift action to grant any weapon he is holding a +1 enhancement bonus for 1 minute. For every four levels beyond 1st, the weapon gains another +1 enhancement bonus, to a maximum of +5 at 17th level. These bonuses can be added to the weapon, stacking with existing weapon enhancement to a maximum of +5. Multiple uses of this ability do not stack with themselves.

At 5th level, these bonuses can be used to add any of the following weapon properties: dancing, flaming, flaming burst, frost, icy burst, keen, shock, shocking burst, speed, or vorpal.

Adding these properties consumes an amount of bonus equal to the property’s base price modifier. These properties are added to any the weapon already has, but duplicates do not stack. If the weapon is not magical, at least a +1 enhancement bonus must be added before any other properties can be added. These bonuses and properties are decided when the arcane pool point is spent and cannot be changed until the next time the magus uses this ability. These bonuses do not function if the weapon is wielded by anyone other than the magus.

Para minha leitura, isso sugere que o Magus nunca deveria ser capaz de adicionar vorpal, porque é uma habilidade de +5 e com uma arma precisando de +1, simplesmente não funciona. Eu entendi mal alguma coisa aqui?