mybatis generator 1.3 + mssql 2014 : generator.xml <property name="useGeneratedKeys" value="true" /> not working

mybatis generator 1.3 + mssql 2014 : generator.xml  not working

<table tableName="tb_test" domainObjectName="tb_test" > 
	<property name="useActualColumnNames" value="true"/>
	<property name="useGeneratedKeys" value="true" /> 
</table>

useGeneratedKeys not working 

mapper.xml is

useGeneratedKeys="true" keyProperty="idx" 
is missing at <insert ...>

 <insert id="insert" parameterType="...tb_test">
    <!--
      WARNING - @mbg.generated
      This element is automatically generated by MyBatis Generator, do not modify.
    -->
    insert into Room (idx, testName
      )
    values (#{idx,jdbcType=BIGINT}, #{testName,jdbcType=VARCHAR}
      )
  </insert>

expected 

 <insert id="insert" parameterType="...tb_test" useGeneratedKeys="true" keyProperty="idx" >

 
useGeneratedKeys="true" keyProperty="idx" 
is missing at 

at tb_test idx is not null identity auto increament. 

why???