ON DUPLICATE KEY construct doesn't work correctly when using lower case column names

@Test
    public void testDeleteOnSingleLowerCaseVarcharColumn() throws Exception {
        Properties props = PropertiesUtil.deepCopy(TEST_PROPERTIES);
        Connection conn = DriverManager.getConnection(getUrl(), props);
        conn.setAutoCommit(false);
        String tableName = generateUniqueName();
        String ddl = " create table " + tableName + "(pk varchar primary key, \"counter1\" varchar, \"counter2\" smallint)";
        conn.createStatement().execute(ddl);
        String dml = "UPSERT INTO " + tableName + " VALUES('a','b') ON DUPLICATE KEY UPDATE \"counter1\" = null";
        conn.createStatement().execute(dml);
        conn.createStatement().execute(dml);
        conn.commit();

        ResultSet rs = conn.createStatement().executeQuery("SELECT * FROM " + tableName);
        assertTrue(rs.next());
        assertEquals("a",rs.getString(1));
        assertEquals(null,rs.getString(2));
        assertFalse(rs.next());
        
        dml = "UPSERT INTO " + tableName + " VALUES('a','b',0)";
        conn.createStatement().execute(dml);
        dml = "UPSERT INTO " + tableName + " VALUES('a','b', 0) ON DUPLICATE KEY UPDATE \"counter1\" = null, \"counter2\" = \"counter2\" + 1";
        conn.createStatement().execute(dml);
        dml = "UPSERT INTO " + tableName + " VALUES('a','b', 0) ON DUPLICATE KEY UPDATE \"counter1\" = 'c', \"counter2\" = \"counter2\" + 1";
        conn.createStatement().execute(dml);
        conn.commit();

        rs = conn.createStatement().executeQuery("SELECT * FROM " + tableName);
        assertTrue(rs.next());
        assertEquals("a",rs.getString(1));
        assertEquals("c",rs.getString(2));
        assertEquals(2,rs.getInt(3));
        assertFalse(rs.next());

        conn.close();
    }