PGAdmin and user privileges - what I do wrong?

Hi!

Please help me a little.

I used PGAdmin to administrate my databases.
I created a new user named "zx".

CREATE ROLE zx LOGIN
ENCRYPTED PASSWORD '*'
NOSUPERUSER NOINHERIT NOCREATEDB NOCREATEROLE;

When I want to manually assign this user to a table, I have problem in
the PGAdmin's Privilege tab.
The privileges GroupBox have a ComboBox, named Role. This ComboBox is
not containing the zx user in it's list.

When I write the user (zx) into the combo , then the "Add" button have
been disabled.

I can write only an SQL cmd to add this privilege. When I do it, the
Privilege list extended with this user, I can select it from the combobox.

What I do wrong? Which property I need to set to I can Add privileges to
the tables/objects with this user?

Thanks for your help:
dd