Rostopic reporting incorrect subscriber type

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What would cause rostopic to report an incorrect subscriber message type?

I have an Arduino running rosserial, defining a couple of subscribers like:

void on_motor_rotate(const std_msgs::Int16& msg) {
    nh.loginfo("Rotating...");
}
ros::Subscriber<std_msgs::Int16> on_motor_rotate_sub("motor/rotate", &on_motor_rotate);

void on_debug_level(const std_msgs::Int16& msg) {
    debug_level = msg.data;
}
ros::Subscriber<std_msgs::Int16> on_debug_level_sub("debug_level", &on_debug_level);

void setup() {
    nh.getHardware()->setBaud(115200);
    nh.initNode();
    nh.subscribe(on_motor_rotate_sub);
    nh.subscribe(on_debug_level_sub);
}

and I'm running the ROS node to communicate with my Arduino with the launch file:

<launch>
    <group ns="torso_arduino">
        <node pkg="rosserial_arduino" type="serial_node.py" name="serial_node" output="screen">
            <param name="~port" command="/dev/ttyACM0" />
            <param name="~baud" value="115200" />
        </node>
    </group>
</launch>

However, when I inspect the message types, I get the incorrect values for the first but not the second.

$ rostopic list /torso_arduino/motor/rotate --verbose

Published topics:

Subscribed topics:
 * /torso_arduino/motor/rotate [std_msgs/Empty] 1 subscriber

$ rostopic list /torso_arduino/debug_level --verbose

Published topics:

Subscribed topics:
 * /torso_arduino/debug_level [std_msgs/Int16] 1 subscriber

Notice how they both expect the Int16 type, but the first rostopic call incorrectly claims it expects the Empty type. Why is this?