ROS misses some messages

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Hello everyone. I'm writing a test program, which receives messages from two different topics and stores them in different queues.
The program, works on a while loop and, at every iteration, before checking for the arrival of new messages, it deletes the top elements of the queues if they have both one.
The program subscribes to a third queue, too, that I use to send a termination message.
Here is the code:

#include "/opt/ros/fuerte/include/ros/ros.h"
#include "/opt/ros/fuerte/include/nav_msgs/Odometry.h"
#include "/opt/ros/fuerte/include/geometry_msgs/Pose.h"
#include "/opt/ros/fuerte/include/geometry_msgs/Point.h"
#include "/opt/ros/fuerte/include/std_msgs/String.h"
#include "/opt/ros/fuerte/include/sensor_msgs/LaserScan.h"
#include "/opt/ros/fuerte/stacks/geometry/tf/include/tf/transform_listener.h"

#include "odom_node.h"
#include "scan_node.h"
#include "messageListener.h"

#include "list"
#include "vector"
#include "coord.h"
#include "math.h"
#include "stdlib.h"
#include "iterator"
#include "string"
#include "iostream"
#include "fstream"
#include "string"
#include "sstream"

#include "stdio.h"
#include "iostream"
#include "map"
#include "math.h"
#include "stdlib.h"
#include "string"

using namespace std;

messageListener::messageListener(){
    odomCounter = 0;
    scanCounter = 0;
}

void messageListener::end_loop(const std_msgs::String mes){
    printf("Setting flag\n");
        while_flag = 0;
}

void messageListener::addOdomNode (const nav_msgs::Odometry mes){
    geometry_msgs::Pose robot_pose = mes.pose.pose;
    geometry_msgs::Point robot_point = robot_pose.position;

    odom_node *on = new odom_node();
    (*on).xCoord = robot_point.x;
    (*on).yCoord = robot_point.y;
    (*on).frame_id = mes.header.frame_id;

    double orientation = tf::getYaw(robot_pose.orientation);
    (*on).angle = (float)orientation;

    odomVector.push_back(*on);
    odomCounter++;
}

vector<coord> messageListener::polar2cart(vector<float> v, float a_min, float a_inc, float range_min, float range_max){
    vector<coord> lc;
    for(int i=0; i<(int)v.size(); i++){
        if(v[i]>= range_min && v[i]<=range_max){
            coord *c = new coord();
            (*c).x = v[i]*cos(a_min + a_inc*i);
            (*c).y = v[i]*sin(a_min + a_inc*i);

            lc.push_back(*c);
        }
    }

    return lc;
}

void messageListener::addScanNode (const sensor_msgs::LaserScan mes){
    //printf("scan");
    scan_node *sn = new scan_node();
    (*sn).scan = mes.ranges;
    (*sn).frame_id = mes.header.frame_id;
    (*sn).cartesian = polar2cart(mes.ranges, mes.angle_min, mes.angle_increment, mes.range_min, mes.range_max);

    scanVector.push_back(*sn);
    scanCounter++;
}

void messageListener::listen(int c, char** v){
    while_flag = 1;
    printf("Listening activity begun\n");
    ros::init(c,v, "listener");
    ros::NodeHandle n_odom, n_scan, n_end;

    ros::Subscriber sub_odom = n_odom.subscribe("/odom", 1000, &messageListener::addOdomNode,this);
    ros::Subscriber sub_scan = n_scan.subscribe("/base_scan", 1000, &messageListener::addScanNode,this);
    ros::Subscriber sub_end = n_end.subscribe("/end", 1000, &messageListener::end_loop,this);
    printf("Subscription complete\n");

    while(while_flag){
        if(odomVector.size()>0 && scanVector.size()>0){
            odomVector.erase(odomVector.begin());
            scanVector.erase(scanVector.begin());
        }

        ros::spinOnce();
    }

    printf("Exit from listening\n");
    printf("Ricevuti %i nodi odometrici e %i nodi scansione\n", odomCounter, scanCounter);
    printf("Terminazione in corso con %i nodi odometrici e %i nodi scansione in coda rimasti\n\n", (int)odomVector.size(), (int)scanVector.size());
}

Here, odomCounter and scanCounter are just two counters that I use to count received messages.
After starting the program, I play a bag file, whose information is reported in the following:

ubisum@ubisum ...