Edit in: refocusing on the active/visible viewer... using set_focus( ) fixes the problem NOT the custom container, because refocusing the container introduces another problem...
Grrr, under SAP GUI for HTML the viewer is still "reloaded" (with loss of scroll position an all). What the ...! 
Not the end of the world - it's just that I, and not Hasso, have to explain all of that to the "ladies in customer service". Oh, well, whatever - as long as one starts out with: "Y'all knew already us IT folks ain't exactly your "normal" kind of people, right?" 
Message was edited by: Jānis B