I've installed PostgreSQL and ODBC driver on my computer under Windows 2000 and used MS Access as a client program.
I created tables with varchar(50) primary key, and accessed them with MS Access via ODBC for PostgreSQL creating linking tables.
There was no problem if I inserted latin letters or digits into a primary key of a MS Access linked table. But I tried to insert Ukrainian letters into the primary key via ODBC. I received a strange message from ODBC that some wrong characters encountered.
In pgAdminIII I saw that my records were successfully inserted (even with Cyrillic letters in primary key).
So, I suppose that there are some bugs in ODBC driver, especially in cyrillic letters processing in primary keys.