Android GPS Location Speed Unreliable

Writing a GPS logging application~

I'm finding the values returned by the getSpeed() method on Locations reported by LocationManager are massively unreliable. I'm using LocationManager.GPS_PROVIDER, filtering the Locations provided through onLocationChanged for best accuracy. Even at single digit accuracy levels the speed returned is generally ridiculously high. We're talking up to 200 mp/h (yes I know it's logged in metres/sec) when the phone is stationary.

I'm testing the same code base on two different model Android phones, running two different OS versions, and seeing the same issues so I expect this is a code issue.

What am I missing? I've tried averaging locations over a window of time, to no avail. Am I going to have to work out my own speed values based on distance travelled / time? This would be disappointing.

As you will see, I'm not doing anything special - a little filtering for accuracy, even after this both AverageSpeed and _bestLocation.getSpeed() are regularly unfeasibly high, even when accuracy of the location is good.

public void onLocationChanged(Location location) {
    if (location.getAccuracy() < 25f) {
        _recentLocations.add(location);

        if (_bestLocation == null || location.getAccuracy() <= _bestLocation.getAccuracy())
            _bestLocation = location;
    }

    if ((_bestLocation != null && _bestLocation.getAccuracy() < 10f && _recentLocations.size() >= 10)
            || _recentLocations.size() >= 25)
    {
        int Count = 0;
            float TotalSpeed = 0f;
            float AverageSpeed = 0f;
            for (int i = 0; i<_recentLocations.size(); i++) {
                if (_recentLocations.get(i).hasSpeed()) {
                    Count++;
                    TotalSpeed += _recentLocations.get(i).getSpeed();
                }
            }

        if (Count > 0)
                AverageSpeed = TotalSpeed / Count;
        }
}