BTW what happens to the pax coming from EZE during the 90 min layover in GRU? Do they stay on the plane or have to disembark?[/QUOTE]

During the layover in GRU no one disembarks the plane (apart from passengers with final dest. GRU).

And that is wierd... Few months ago I flew Air China from BCN to PEK. The plane had a simillar stop-over in Vienna. We all disembarked the plane, but were locked in a separate waiting area.