"Permission denied" on public view

Hi there,

I am working on a db application that allows students to choose 
their courses, so I try to design everything securely. However, it 
seems to be that secure, that users don't have access on a certain 
view, which I don't understand.
To track down and understand the problem, I devised a little model, 
which is supposed to store information about different cars of 
different postgres users:

/* Main Table */
CREATE TABLE data(owner NAME, car TEXT);
CREATE SEQUENCE datalog;
CREATE RULE ins_data AS ON INSERT TO data DOSELECT NEXTVAL('datalog');
GRANT ALL ON datalog TO PUBLIC;

/* Public View */
CREATE VIEW publicdata AS SELECT * FROM data WHERE 
owner = USER;
CREATE RULE ins_publicdata AS ON INSERT TO publicdata DO 
INSTEADINSERT INTO data(owner, car) VALUES(USER, new.car);
GRANT SELECT, INSERT ON publicdata TO PUBLIC;

The datalog sequence is used to detect and track changes in the 
data table. Everything works fine when I use a Postgres superuser, 
for example an insert like:INSERT INTO publicdata(car) VALUES('Ford');

However, when I try the exact same statement with a different user, 
I get the error message:ERROR:  data: Permission denied.

When I remove the ins_data rule, the INSERT works for the other 
users as well. Does the rule need access to the data table? Is this 
a bug or am I doing something wrong?

I appreciate your help, Martin Kresse