[web2py] duplicate entry error for update_or_insert

[simon]

I get a duplicate entry error on an update_or_insert. First record with 
category_id=1 is inserted fine. Second record with category_id=2 fails 
saying"Duplicate entry '0-1' for key 'PRIMARY'"

Model:
      web.define_table('category_description',
           Field('category_id', 'integer', notnull=True, writable=False),
           Field('language_id', 'integer', notnull=True, writable=False, 
default=1),
           Field('name', 'text', length=255, notnull=True),
           Field('description', 'text', length=65535, notnull=True),
           primarykey=['category_id', 'language_id'])

Controllert:
        wd=web.category_description
        wd.update_or_insert(wd.category_id==category.webid,
                      name=category.name,
                      description=category.description)

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