Repaint of ADDMENU menus in windows

[pamoroso]

I'm studying the user interface of the command window of the GRAPHCALLS LispUsers module, specifically the repaint of the menus added inside the window by ADDMENU. The relevant code sets the REPAINTFN of the window to a function that calls MENUREPAINTFN, and does other things apparently unrelated to the menus.

I tried to recreate the repaint behavior with this code:

4_ (SETQ W (CREATEW NIL "Repaint Test"))
{WINDOW}#122,27000
5_ (SETQ M (create MENU ITEMS _ '(One Two Three Four Five) TITLE _ "Menu"))
{MENU}#131,131130
6_ (ADDMENU M W)
{WINDOW}#122,27000
7_ (WINDOWPROP W 'REPAINTFN (FUNCTION (LAMBDA (WINDOW) (CLEARW WINDOW) (MENUREPAINTFN WINDOW))))
(MENUREPAINTFN)

which yields this window with a menu at the lower left corner:

However, when I reshape the window the menu is cropped and not at the expected location:

What am I missing?

[pamoroso]

I forgot to mention that adding a CLEARW call just before the MENUREPAINTFN call doesn't help.