[Lazarus] F1 on Linux I got 255

[Andrea Mauri]

Dear all,

lazarus 1.4.4 fpc 2.6.4
Under linux VirtualBox if I launch my application and press F1 I got key 
=255 instead key = 112

procedure TfrmMainMenu.FormKeyDown(Sender: TObject; var Key: Word;
   Shift: TShiftState);
begin
   // check for F1
   if (Key = VK_F1) then
   begin
	//dosomething
   end;
end;

why?

Lazarus Ide seems to properly detect F1. My application not.

Any hint?
Andrea Mauri