I read about Zbar two weeks ago in http://onsoftware.softonic.com/50-mejores-utilidades-pequenas . I thought that Zbar could fix the problem (how would win7 handle a taskbar double the size of the active monitor?) but didn't give it a try.
When I read your tip, I immediately installed it and end of the problem. As many of the users have pointed out here, it is a software issue: Zbar forces indeed a "re-detection" of the monitors, I can still listen to the hardware connect/disconnect sounds, but this is far much better than buying new hardware.
Thanks again :-)