The grid is usually resized whenever the window is resized. This means there will be more or fewer grid squares than there were previously. After the resizing all grid squares are marked CM_AVAIL, regardless of their state before the resizing. The application must send another CM_SETGRIDINFO message to re-mark the squares as available or unavailable. Re-marking the grid squares is necessary only if the application wants to use the CMA_USER arrange pattern, otherwise the notification can be ignored.