[SDL] Lost surfaces

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Hello all,
        
     I was trying to deal with those "lost surfaces" that I get after
   switching to another application. Here is what I would like to
   know:
   
       - what surfaces can be lost?
       - where must I check that?
       - how should I resore them? Just reload?

     My OS: WinXP Pro
     My compiler: MS VS 2003

-- 
Thanks for attention,
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