Forms in menu_edit_item() and menu_form_node_form_alter() functions do not specify #maxlength for menu link titles, so the default of 128 characters is used. Menu item title can contain 255 characters as defined in 'menu_links' DB table schema. So the limitation of 128 characters is meaningless (set by Form API defaults), and I suggest to set #maxlength to 255 explicitly in forms containing menu link titles.
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