Focus does not move to the first item of the navigation view when in LeftMinimal mode and an item header is present.

[EriWong]

Describe the bug
The first time a navigation view in LeftMinimal mode is opened via keyboard, and the first item is a item header, focus does not move to the first item non-header item in the list. Every other time it is opened, focus moves correctly.

Steps to reproduce the bug

Steps to reproduce the behavior:
xaml for minimal repro:

        <muxc:NavigationView PaneDisplayMode="LeftMinimal" >
            <muxc:NavigationView.MenuItems>
                <muxc:NavigationViewItemHeader Content="header" ></muxc:NavigationViewItemHeader>
                <muxc:NavigationViewItem Content="item" ></muxc:NavigationViewItem>
            </muxc:NavigationView.MenuItems>
        </muxc:NavigationView>

1. Tab to the navigation view
2. hit enter to open it
3. dismiss the menu
4. repeat steps 1 and 2, and note that from here on in, "item" gets focus when the navigation view is opened.

Expected behavior
Focus should move consistently each time the navigation view is opened. I believe the behavior after the first time the navigation view is opened is correct.

Version Info

NuGet package version:
Microsoft.UI.Xaml 2.1.190405004

Windows 10 version	Saw the problem?
Insider Build (xxxxx)
October 2018 Update (17763)	Yes
April 2018 Update (17134)
Fall Creators Update (16299)
Creators Update (15063)
Anniversary Update (14393)

Device form factor	Saw the problem?
Desktop	Yes
Mobile
Xbox
Surface Hub
IoT

Additional context