Tray icon keyboard access: Up/Down keys and Esc do not work (popup-menu frozen)

[rparenzs]

On Windows XP SP3, if I use the Win+B key combo to jump the focus to the tray, I can use the Left/Right cursor keys to select the Thunderbird minimized icon and hit the context-menu key (or Shift+F10) to access its right-click menu. But once this happens I cannot use the Up/Down cursor keys to select an item, or Esc to close the menu, which becomes stuck open unless I use the mouse.

This was last working on v1.1.2.1-signed but failed when I updated to 1.3.1 or 1.3.2.