Changing the icon of a MenuExtra doesn't change the menubar icon

When I change (from the preferences) the icon of a MenuExtra, the change is visible in the Finder and in the dialogs sent by that SSB (like the confirmation prompt when closing a multi-tabs window) but the icon in the menubar remains the same, even after quitting and re-launching the SSB.

On closer examination, this appears to be caused by the file .../Contents/Resources/icon.tiff not being updated when appl.icns is.