@BetterRed: gonna check this! Right now I am downloading and installing English-US locale for the Win 8 computer

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The strangest thing is that sorting works just fine for any other columns.
// EDIT
@BetterRed: I've checked my Windows settings. Well, as expected they're a bit different: ',' as the decimal symbol, [blank] as the digit grouping symbol, ';' as the list separator. However, this has never seemed to be an issue for Calibre, which uses '.' as the decimal symbol and ',' as the digit grouping symbol (probably because I have Calibre in English).