portal and many-to-many relationship
it is my first post here, so the problem I want to solve is quite easy. In order to present it I've created a very simple data-base, which ilustrates the problem. You can find it here: http://www.sendspace.com/file/es50sk .
In the sample data base there are two main tables: people and cities. The data-base is designed to show cities visited by certain people. It is obviously many-to-many relation so an additional join table was created.
I would like to enter all data in one-place so inside the person layout I've created the portal with a data from the City table. It works, but it muliplies/duplicates the city records (picture below), so actually it works as one-to-many relationship. Is there any way to avoid the problem of record duplication?
I would like to add that I cannot create the list of all peoples and all cities before creating a portal. All data should be entered via the portal. Thanks a lot for your help in advance. I have tried to search information virtually everywhere, but I haven't found it although I feel that the solution must be so easy.