Can't make <data-prepend> work in a <select data-role="select" multiple data-clear-button="true">

Metro UI 5.1

If a include data-pretend into select tag, it NOT WORK, NOT SHOW the prepend string: <select data-role="select" multiple data-clear-button="true" data-prepend="Something>">

If I delete multiple data-clear-button from select tag it WORK and SHOW the prepend string <select data-role="select" data-prepend="Something>">

Please, how to fix it?