Is this a glitchy ADS-B signal? I was looking through my virtual radar logs one of the days and found this "glitchy" ADS-B behavior.  I am almost 100% sure that this is not due to my antenna or setup since two independent different radars confirmed this weird behavior from FlightRadar24.  Also A/C before and after this one did not exhibit this behavior.


Does anybody have any thoughts as to what may be happening???
Why is the "skew" at seemingly same angle?  Is that anything?
In light of MH370, does this happen often, how reliable is that GPS data?


Tail # N657UA
Boeing 767-300
Typical route between EGLL and KORD

Time of occurrence is approximately: 3/16/2014 6:09pm CST

I have also verified FlightAware is ALSO showing the same weird glitch.  

See below "yellow" highlighted airplane:


Same A/C from FlightRadar24:


UPDATE:

This seems to be related to THIS aircraft.  The explanations given (GPS->INS->GPS switching) still applies in my opinion, but wanted to give another screen shot.  Here it is today (3/30/2014) and again displaying this behavior - should their maintenance department be alerted to adjust their GPS antenna??
This is a classic example of fallback to INS. Most of the track data is coming from GPS. For some reason the GPS signal is lost momentarily causing a fall back to INS. The INS is offset by about 1km to the Northeast, which appears as a jump. Next position report is from the GPS again, in line with the original track. This happens several times. 

In the transmitted data these spikes will be flagged as data of low integrity. This allows for filtering them out.