On a single-value list-picker, if I choose a value and then I click on the "cross" icon on the right of the selection (to clear the selection), it will look visually empty (without selection) but the underlying <select> element will have a value. Its value will be the first possible, non-disabled, <option>.
The way to workaround this issue is to add an empty option like <option value=""></option> (see request #32627). Nonetheless, the list-picker should not act like there is no value. It should stay in sync with its <select> and show the first non-disabled option as selected.