[amibroker] Problem with SetForeign and TimeFrameGetPrice on Intraday-Chart

[bleifish]

I'm trying to plot the percentual gain of multiple symbols from 
Watchlist Nr. 0 plotted on the same intraday chart. 

But I've been sticked in a problem, that I don't understand:

I have "ASTIZ" and "LTRE" on my watchlist 0
and this is my code:

list = GetCategorySymbols( categoryWatchlist, 0 );

symbol = StrExtract( list, 0 );
if ( symbol != "" )
{
  SetForeign( symbol, True, True ); 
  dayOpen = TimeFrameGetPrice( "O", inDaily, 0 ); 
  Plot( dayOpen,symbol,colorRed,styleLine|styleDots);
  RestorePriceArrays( True );
}

The Open value for "ASTIZ" on 14. december .2007 was 10.06.
This will be corretly plotted when symbol "ASTIZ" is seleced.
But when I select "LTRE" the value 10.5 has been plotted.

Any idea, what's going on?

Thank you in advance!