Usage of Time Synchronizer with rosbag

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Hi there, I am writing a ros node which subscribe to 3 lasers range finders (Sick LMS), and do some processes on them. I am runing on ros Fuerte.

So I use a message_filter::TimeSynchronizer to synchronize them, and to centralize all the datas in an unique callback.

class LaserSubscriber
{
    typedef message_filters::Subscriber<sensor_msgs::LaserScan> tLaserSub;
    typedef message_filters::sync_policies::ApproximateTime<sensor_msgs::LaserScan, sensor_msgs::LaserScan,
                                                            sensor_msgs::LaserScan> tApproxTimeLaser;
    typedef message_filters::Synchronizer<tApproxTimeLaser> tSynchronizer;
public:
    LaserSubscriber();
    void OnNewScans(LaserListener::tLaser &_scanVert1, LaserListener::tLaser &_scanVert2,
                    LaserListener::tLaser &_scanHoriz);
//...
};

So as you can see, I am using the ApproximateTime sync policy.

When I play with rosbag, I have a strange behaviour. If I launch rosbag play with the "loop" and "clock" options, the first loop will works well, but not the second one. In the second loop, the call back is never called.

I think it's because the synchronizer is waiting for a data which will never be published. When /clock is "x" (the end of my rosbag", and my rosbag restart, /clock is "y" and y < x, so the synchrnonizer seems to wait for a data stamped with something greater than x (that is what we want when we use a synchroniser).

TF have the same problem, but TF is very smart, it detect a jump in time and reset the cache.

My reasoning is it good ? Does the synchronizer can do the same ? Is it possible to reset manualy a synchronizer ?

Regards,