IBController retrieves futures' expiry dates different than shown

Does anyone know if this is normal behaviour? The futures expiry dates that IBController reads are sometimes different than those shown in the app itself

Thank you

//read tickers IB format
#include <TickersIB.afl>  // var: tib

//start interface
ibc = GetTradingInterface("IB"); 
//if connected read data
if ( ibc.IsConnected() )
	ibc.sleep(1000);  //need to wait for TWS otherwise doesn't read anything
	Expiry = ibc.GetPositionInfo( tib, "Expiry");

Filter = Status( "lastbarinrange" ); 


@Armin_Tamzarian - I could not find this documented either. For the ES, the official expiry date from the CME the 2021-09-17. If I had to guess, 2021-09-16 might be the last date that IB allows you to trade it.