Wrong publishing rate using ros::Rate

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Hi, I was trying to use ros::Rate to control the publishing rate. However for some reason, the publishing rate obtained is not the one I expected.

Here's my code:

ros::Publisher pub1,pub2;
ros::Rate *r1,*r2; 

void callbackInt(const std_msgs::Int16ConstPtr& msg) {
    pub1.publish(msg);
    r1->sleep();
} 

void callbackString(const std_msgs::StringConstPtr& msg) {
    pub2.publish(msg);
    r2->sleep();
} 

int main (int argc, char** argv) {

    ros::init (argc, argv, "test");
    ros::NodeHandle nh;

    ros::Subscriber sub = nh.subscribe ("/int", 1, callbackInt );
    pub1 = nh.advertise<std_msgs::Int16> ("/pubInt", 1);

    ros::Subscriber sub2 = nh.subscribe ("/string", 1, callbackString );
    pub2 = nh.advertise<std_msgs::String> ("/pubString", 1);

    ros::Rate rate(5);
    r1 = &rate;
    ros::Rate rate2(5);
    r2 = &rate2;

    ros::spin();
}

The code should be pretty straightforward: basically I'm subscribing to two different topics (/int and /string) and re-publishing on different topics (/pubInt and /pubString) at different 5 hz (their original rate was different).

However, if I try to check the actual rate with rostopic hz I get 5 hz for /pubInt but half the rate (2.5) for /pubString. Any suggestion? Am I doing something wrong?