Currently SQLObject determines the joinColumn for MultipleJoin from the name of the table.
In the documentation it is recommended to use "user_table" as a table for an class called User. When one now creates another class, e.g. Address that has a ForeignKey from User in a column called "user", one needs to add joinColumn='user_id' to the MultipleJoin definition within the User class, otherwise one only gets a totally strange python traceback, when one tries to access u.addresses.
I attached a simple example, that makes it more clear, where the problem here is.
I use python-sqlobject-0.9.2-1.fc7 from Fedora.