setUserTrackingMode display troubles sometimes occuring

Question

I have a weird issue (concerning the displaying of my current location) with the call of the method of MKMapView :

- (void)setUserTrackingMode:(MKUserTrackingMode)mode animated:(BOOL)animated

My map well display my location with the blue dot, but there is an issue occuring "sometimes" with the center and zooming features of this method :

• Sometimes the view start zooming and then it quickly come back to it's start position, so the view is not centered and zoomed on my current location.
• The other times it works : the view is centered and zoomed on my current location.

Note that this issue has not the same occurence between Simulator/iPhone(5). On my iPhone, this issue only happen when I launch the view for the 1st time. And sometimes, at the 1st time, it works…

See the screen when it works, it's well centered :

And when the trouble occurs :

In the viewDidLoad of my MKMapView, I placed :

[map setUserTrackingMode:MKUserTrackingModeFollowWithHeading animated:YES];

NOTE: map has been synthesized.

I also checked in the method :

- (void)mapView:(MKMapView *)mapView didUpdateUserLocation:(MKUserLocation *)userLocation
{
    NSLog(@"didUpdateUserLocation : lat : %f, long : %f", userLocation.location.coordinate.latitude,
                                                   userLocation.location.coordinate.longitude);
}

And the coordinates are the good ones (thoses of my current location).

I searched and searched on the site, but I couldn't find my answer.

Anyone experienced the same issue ?

I wanted to know if it's a bug or an error from me.

Thanks for ideas and help.

EDIT : A new behaviour just appeared : after have quickly moved back to the starting display location (my issue), the view centered and zoomed on my current position as soon as it moved back !..

And sometimes i get the interference message like there : http://hillcrestlabs.com/makingmotion/wp-content/uploads/2012/06/compass-interference-v2.png.

Maybe my theses issues have a link with this interference problem ?

I tried to get away with my iPhone from computers and working room but the issue is still here… Should I go farther ?