Changing Delphi styles at runtime doesn't allow dropping files to the form

Question

I have the following procedure that allows droping files from windows, the dropping works just fine but when I change the style at runtime using (TStyleManager.TrySetStyle(styleName)), the form accept no more dropping! what is wrong here exactly?

public //public section of the form
...
procedure AcceptFiles( var msg : TMessage ); message WM_DROPFILES;

...

procedure TMainFrm.AcceptFiles(var msg: TMessage);
 var
   i,
   fCount     : integer;
   aFileName : array [0..255] of char;
begin
   // find out how many files the form is accepting
   fCount := DragQueryFile( msg.WParam, {uses ShellApi is required...}
                            $FFFFFFFF,
                            acFileName,
                            255 );

  for I := 0 to fCount - 1 do
  begin
    DragQueryFile(msg.WParam, i, aFileName, 255);
    if UpperCase(ExtractFileExt(aFileName)) = '.MSG' then //accept only .msg files
    begin
       if not itemExists(aFileName, ListBox1) then// function checks whether the file was already added to the listbox
       begin
        ListBox1.Items.Add(aFileName);

       end
    end;
  end;
  DragFinish( msg.WParam );
end;

...

procedure TMainFrm.FormCreate(Sender: TObject);
begin
  DragAcceptFiles( Handle, True ); //Main form accepts the dropped files 
end;