<win-pivot> doesn't output properly.

[realgoodappz]

Placing this into my HTML from the example

<win-pivot>
    <win-pivot-left-header>Custom Left Header</win-pivot-left-header>
    <win-pivot-item header="'First'">
        Pivots are useful for varied content
    </win-pivot-item>
    <win-pivot-item header="'Second'">
        This Pivot  is boring however, it just has things like data bindings: {{ratings.length}}
    </win-pivot-item>
    <win-pivot-item header="'Tail...'">
        Because it's only purpose is to show how to create a Pivot
    </win-pivot-item>
    <win-pivot-right-header>Custom Right Header</win-pivot-right-header>
</win-pivot>

Doesn't output anything within the headers. The HTML outputs as shown in both Chrome and Edge.

<div class="win-pivot-header-items">
<div tabindex="0" aria-hidden="true"></div>
<div tabindex="0" class="win-pivot-headers"></div>
<div tabindex="0" aria-hidden="true"></div>
</div>