Metatrader History Center shifts the time stamp .

I know it warns me. But why does it do it.....I would like 2 know the logic of this shift.

Let me explain how I found out when it shifts. I want 2 make sure my lodgic is sound 

Step one I Down loaded from Reuters Eikion  EE page all of the news events back 2 2005. These are time stamped EST with day light savings time on . 

Step two .On Oanda Demo Server GMT 5 ( est time ). I cleaned these directories of all data 

 \history\OANDA-GMT-5 Practice of all data. 

\history\downloads

\history\deleted 

 Tester I have not used it was not cleared but has no data in it

Step Three . I waited until the week end made sure I was not logged in and had a comm error in the connection status. The point of this is 2 insure That I only got Data from Metatrader and not Oanda 

Step Four. I set the tools options charts Max  bars 2 10000000 and Max bars on chart 2 10000000

Step Five. exit and reenter

Step six down loaded by hand all the data from metatrader. Noting the down load site that was accessed. 

Step Seven. Exit come back in  

Step Six Imported the  data from Reuters and labeled all non farm events. 

Step Seven started spot checking  Years and months randomly picking dates before Daylight savings and after for the Reuters Instrument code USNFAR=ECI. " US NON FARM ". I also dumped the data six bars before the even and six bars after the event on. every Event 2 check the for volatility High - Low of each bar. It is easy 2 stop the news event in the data set. I also labeled it on the chart.  

Now the issue Non farm on 11/7/2014 8:30 est  is fine... on 12/5/2014 8:30 est The data set shifts by 12 Bars.Though 2014 Both before and after daily light saving it stays 12 bars......... I have only spot check the records.

My question is Why ?

When is the exact date it shifts. ?

Does it do any other times.?  

I have not checked every Bar. It did not sound like an enjoyable thing 2 do. Any ideas would be welcome