So, when I give the following command: / lp user (nick) parent addtemp vip, the player receives the group all right, but when I remove with / removetemp he continues with the group like this: group.vip world = spawngeral, how could I not automatically give it to the player?

Most likely another plugin assigning the group again in another world, probably via Vault if the world is being added. This isn't being done by LuckPerms though.