Gazebo7 IMU plugin - No TF between base_link and imu_link

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My environment is Ubuntu 16.04, running Gazebo7 with ROS Kinetic.

The following gazebo imu plugin is configured using via a xacro. The xacro also uses the diff drive controller plugin. Everything loads well, except I cannot see the TF between base_link and imu_link via view_frames or tf_monitor. I do however see the the the TF between the wheels and base_link. Am I missing something? The same xacro works well in Gazebo 2.2.3 and ROS indigo.

  <gazebo>
    <plugin name="imu_controller" filename="libgazebo_ros_imu.so">
      <alwaysOn>true</alwaysOn>
      <updateRate>30</updateRate>
      <bodyName>imu_link</bodyName>   <!--imu_link -->
      <topicName>imu/data</topicName>
    <serviceName>imu/is_calibrated</serviceName>
      <gaussianNoise>0.1</gaussianNoise>
    <xyzOffsets>0 0 0</xyzOffsets>
    <rpyOffsets>0 0 0</rpyOffsets>
    </plugin>
  </gazebo>

tf_monitor output:

Frames:
Frame: base_link published by unknown_publisher Average Delay: 0.000166667 Max Delay: 0.001
Frame: left_front_wheel_link published by unknown_publisher Average Delay: 0 Max Delay: 0
Frame: left_rear_wheel_link published by unknown_publisher Average Delay: 0 Max Delay: 0
Frame: right_front_wheel_link published by unknown_publisher Average Delay: 0 Max Delay: 0
Frame: right_rear_wheel_link published by unknown_publisher Average Delay: 0 Max Delay: 0

All Broadcasters:
Node: unknown_publisher 41.365 Hz, Average Delay: 0.000125 Max Delay: 0.001