QLibrary getFileName method returns "DLL" on Windows7 and "dll" on Vista

// full filename has "dll" extension. Example: c:/project/test.dll
QString filename = "c:/project/test";
QLibrary lib(filename);
if (! lib.load())
      return false;
QString fname = lib.fileName();
lib.unload();

// in Windows Vista returned fname has "dll" extenstion; in Windows 7 it has "DLL" extension. Therefore subsequent call "isLibrary" fails because it checks for lower-case "dll";